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\title{Do the Right Thing: Experimental evidence that preferences for moral behavior, rather than equity or efficiency per se, drive human prosociality}

\author{
Valerio Capraro\thanks{Department of Economics, Middlesex University, London}
\and
David G. Rand\thanks{Department of Psychology, and Department of Economics, School 
of Management, Yale University.}
}

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\newcommand{\jhead}{Judgment and Decision Making, Vol.~13, No.~1}
\newcommand{\jdate}{January 2018}
\pagestyle{myheadings} \markright{\protect\small \href{\jref}{\jhead},
  \jdate \hfill Moral preferences drive human prosociality \qquad}
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\begin{onecolabstract}
%\end{latexonly}
  Decades of experimental research show that some people forgo
  personal gains to benefit others in unilateral anonymous
  interactions. To explain these results, behavioral economists
  typically assume that people have social preferences for minimizing
  inequality and/or maximizing efficiency (social welfare). Here we present data that cannot be explained by these standard social preference models. We use a “Trade-Off Game” (TOG), where
  players unilaterally choose between an equitable option and an
  efficient option. We show that simply changing the labelling of the
  options to describe the equitable versus efficient option as morally
  right completely reverses the correlation between behavior in the
  TOG and play in a separate Dictator Game (DG) or Prisoner’s Dilemma
  (PD): people who take the action framed as moral in the TOG, be it
  equitable or efficient, are much more prosocial in the DG and
  PD. Rather than preferences for equity and/or efficiency \textit{per
    se}, our results suggest that prosociality in games such as the DG
  and PD are driven by a generalized morality preference that
  motivates people to do what they think is morally right.

\smallskip
\noindent
Keywords: prosociality, morality, equity, efficiency
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{\renewcommand{\thefootnote}{}

\footnotetext{

Copyright: \copyright\ 2018.
The authors license this article under the terms of the
\href{http://creativecommons.org/licenses/by/3.0/}{Creative Commons
  Attribution 3.0 License.}
}}

\saythanks

\section{Introduction}

\renewcommand{\baselinestretch}{1.03} \large\normalsize

Humans regularly pay costs to benefit others. This prosocial (or
“cooperative”) behavior is central to the success of our personal
relationships and the functioning of our societies, and is more
important than ever in the face of global-level challenges like
resource conservation and climate change. Thus a great deal of research
across the natural and social sciences has sought to understand what
motivates people to be prosocial. 

One answer to this question is offered by work demonstrating myriad
long-run benefits that accrue from helping others: if I pay a cost to
give you a benefit today, you may be more willing to help me in the
future, as may others who observe my action (Axelrod \& Hamilton, 1981;
Dal Bó, 2005; Fudenberg \& Maskin, 1986; Nowak, 2006; Nowak \& Sigmund,
2005; Rand \& Nowak, 2013; Trivers, 1971). Thus, in situations where
there are future consequences for current actions. pure self-interest
can often motivate prosocial behavior (e.g., Dreber, Fudenberg, and Rand
(2014). 

However, people are sometimes willing to be prosocial even when doing so
is not self-interested. For example, decades of research show that many
people will pay costs to benefit strangers in one-shot anonymous
laboratory experiments (Camerer, 2003; Dawes \& Thaler, 1988), and
recent work has shown that prosocial behaviors in different economic
games are typically correlated, both in the same session and over time
(Capraro, Smyth, Mylona \& Niblo, 2014; Capraro, Jordan \& Rand, 2014;
Peysakhovich, Nowak \& Rand, 2014; Reigstad, Strømland \& Tinghög,
2017). This suggests the existence of stable individual differences in
prosociality, what has been dubbed a “cooperative phenotype”
(Peysakhovich et al., 2014). To explain these observations, behavioral
economists typically employ social preference models (Camerer, 2003;
Camerer \& Fehr, 2004). These models argue that people care about more
than just their own material payoffs. 

Widely used social preference models, especially for analyzing
unilateral giving decisions, focus exclusively on \textit{outcomes}.
They assume that people get psychological benefits (utility) from the
payoffs of others (i.e., are “altruistic” or care about efficiency, the
total payoff of all players) (Charness \& Rabin, 2002; Engelmann \&
Strobel, 2004); and/or incur psychological costs (disutility) from when
payoffs are unequal between themselves and others (i.e., are “inequity
averse”) (Bolton \& Ockenfels, 2000; Fehr \& Schmidt, 1999). (There are
also reciprocity-based social preference models where people get
utility from rewarding positive actions and punishing negative actions
[e.g., Dufwenberg \& Kirchsteiger, 2004; Falk \& Fischbacher, 2006; Rabin,
1993)], but these theories do not make clear predictions about behavior
in unilateral decisions, which are our focus; thus we restrict our
attention to purely outcome-based preferences related to efficiency and
inequity.)

These social preference models based on efficiency and inequity have
helped to organize a great deal of experimental data on prosociality in
economic games. In these games, such as the Prisoner’s Dilemma (PD) and
the Dictator Game (DG), subjects choose between selfish options
that maximize their own payoff and prosocial options that increase the
other’s payoff and/or reduce inequity. By stipulating that people vary
in the weights placed on efficiency and inequity in their utility
functions, one can account for variation in behavior in these games. 

Despite their success and widespread use, however, many scholars have
argued that human prosociality is not, in fact, driven by outcome-based
preferences. An alternative on which we focus here is the idea of a
generalized morality preference – that is, the proposal that people
vary in the utility they get from “doing the right thing” broadly,
instead of caring specifically about efficiency and inequity (e.g.,
Alger \& Weibull, 2013; Baron, 2008; Bicchieri, 2005; Brekke,
Kverndokk \& Nyborg, 2003; Eriksson, Strimling, Andersson \&
Lindholm, 2017; Huck, Kübler \& Weibull, 2012; Jordan, Mullen \&
Murnighan, 2011; Krupka \& Weber, 2013; López-Pérez, 2008; Mazar, Amir,
\& Ariely, 2008; Sachdeva, Iliev \& Medin, 2009; Weber, Kopelman \&
Messick, 2004). A variety of sources – which sometimes, but not always,
include the extent of efficiency or inequity – influence which action
is “right” in a given situation. 

Here, we present new experimental evidence showing the limitations of
outcome-based social preference models of equity and efficiency
concerns, and supporting a generalized morality preference account. We
do so by leveraging individual differences in prosociality in canonical
games (the Prisoner’s Dilemma, PD, and Dictator Game, DG).
Specifically, we examine the correlation between an individual’s
prosociality in these games and their play in a “Trade-Off Game” (TOG)
which pits equity against efficiency – and, critically, how this
correlation varies with the framing of the TOG. 

In the TOG, players unilaterally determine the payoffs of themselves and
two others, and can choose between an option that is more equitable
(all three people earn 13 Monetary Units (MUs)) and an option that is
more efficient (the player receives 15 MUs, while the other two people
receive 13 MUs and 23 MUs respectively).

If a stable outcome-based preference for efficiency/altruism drives
cooperation in the PD and giving in the DG, then people who are more
prosocial in the PD and DG should be more likely to choose the
efficient option in the TOG. Conversely, if a stable outcome-based
preference for inequity aversion drives cooperation in the PD and
giving in the DG, then people who are more prosocial in the PD and DG
should be more likely to choose the equitable option in the TOG. In
either case, these correlations should not be influenced by how the TOG
is framed.

The predictions of a general morality preference, however, are
different. Because neither option in the TOG is clearly more prosocial
than the other, having a morality preference should not lead to a
consistent, clearly defined favoring of one option over the other.
Instead, play should be heavily influenced by the framing (despite the
irrelevance of beliefs): subjects should be much more likely to
choose the option which is presented as the morally appropriate. As a
result, if a general morality preference drives prosociality in the PD
and DG, then people who are more prosocial in the PD and DG should
choose whichever TOG option is presented as morally right, regardless
of whether it is more equitable or efficient. 

In this paper, we present six experiments testing these diverging
predictions. The results cannot be explained by standard social
preference models based on preferences over outcomes, but they are
consistent with the predictions of the general morality preference
account.

\section{Study 1}

In Study 1, we examine how framing affects play in the TOG, as well as
the relationship between TOG play and play in a PD. To do so, we
compare two different TOG frames designed to suggest that one choice
versus the other is morally appropriate – and thereby to resolve the
ambiguity that the equity/efficiency trade-offs creates about what the
“right thing to do” is in the TOG. That is to say, we purposely create
an experimenter demand effect --- i.e., provide “cues about what
constitutes appropriate behavior” (Zizzo, 2010) – for either the
equitable or efficient TOG choice, and observe the impact on TOG
behavior and cross-game correlation in play. 

Experimenter demand effects are typically seen as problematic because
experimenters are usually trying to assess how subjects respond to
the details of their design (e.g., the payoffs in an economic game).
Thus, injecting cues about which option is appropriate creates an
undesirable alternative source of variation in behavior, which is
particularly problematic when the choice suggested by the demand effect
is the same as the one hypothesized to be caused by the experimental
manipulation (in which case one cannot tell if the result is due to the
manipulation or the demand effect). This is not, however, a problem for
the experiments we present in this paper. On the contrary, what we are
seeking to study is precisely the effect of giving information about
the appropriateness of different options. The demand effect \textit{is}
our manipulation, rather than being a confound.

\renewcommand{\baselinestretch}{1.05} \large\normalsize

\subsection{Subjects}

We recruit N = 498 subjects living in the US at the time of the
experiment using the online labor market Amazon Mechanical Turk
(AMT)\footnote{Experiments on AMT are easy to implement and fast and
  cheap to realize. At the same time, numerous studies using economic
  games have found that data gathered on AMT are of no less quality
  than those collected using physical laboratories (Amir, Rand \& Gal,
  2012; Horton, Rand \& Zeckhauser, 2011; Suri \& Watts, 2011).\par }.

\begin{figure}[t]
\includegraphics[clip=true,width=\columnwidth]{fig1.eps}
\caption{Results of Study 1 (N=498): \textbf{Subjects who make the
    nice choice in the Trade-Off Game, whichever that is, cooperate
    more in the Prisoner’s Dilemma.} We plot average cooperation in
  the Prisoner’s Dilemma as a function of the choice made in each of
  the two frames of the Trade-Off Game. Error bars represent +/- 1
  SEM. Subjects making the “nice” choice in the Trade-Off Game,
  whichever that is, cooperate more in the Prisoner’s Dilemma than
  subjects who make the “non-nice” choice. Since the nice choice in
  the Equalize frame is economically equivalent to the non-nice choice
  in the Give frame, this correlation cannot be explained by
  outcome-based preferences and suggests that a substantial proportion
  of cooperators is motivated by a preference for “being nice”.}
\end{figure}

\subsection{Procedure}

Subjects are randomly assigned to one of four conditions. In the
\textit{PD-Give} condition, subjects first play the Prisoner’s dilemma
(PD), and then play the Trade-Off game (TOG) in the “give frame”. In
the PD, subjects are given \$0.10 and asked whether they want to “keep
it” or “hand it over” to the other subject. In the latter case, the
other subject would earn \$0.20. Subjects are informed that the
subject they are matched with is simultaneously facing the same
decision. In the TOG in the “give frame”, subjects in the role of
Player A are grouped with two other subjects (Player B and Player C)
and told that all three players start with \$0.13.  Subjects can
choose “to be nice” in which case they gain \$0.02 and player B gains
\$0.10, or “not to be nice”, in which case nothing happens and all
three players remain with \$0.13. Subjects are aware that Player B and
Player C are not making any decision. In the \textit{PD-Equalize}
condition, subjects first play the PD and then play the TOG in the
“equalize frame”. The “equalize frame” of the TOG is economically
identical to the “give frame”, but the names of the strategies are
switched: subjects in the role of Player A are told that they start
with \$0.15, player B starts with \$0.23, and player C starts with
\$0.13, and that they can choose “to be nice” by giving up \$0.02 in
order “to restore equality” or “not to be nice”, in which case nothing
happens. The \textit{Give-PD} and the \textit{Equalize-PD} conditions
are identical to the PD-Give and PD-Equalize conditions, respectively,
apart from the order in which the games are played. Our main analyses
collapse over game order, which does not interact with TOG framing
(see the Supplementary Information,
\href{http://journal.sjdm.org/17/171107}{SI}). In this and in the
following experiments, standard comprehension questions are asked
right after presenting the instructions of the Prisoner’s dilemma and
the Dictator game. Subjects failing any comprehension question are
automatically excluded from the survey. After the data are collected,
bonuses are computed and paid, on top of the participation fee
(\$0.50). No deception is used. Full experimental instructions are
reported in the Appendix.

\subsection{Results}

As predicted by our account, but not the equity and efficiency
preferences account, the frame has a dramatic impact on TOG play:
under the Equalize frame, 47.2\% of players choose the equitable
option, compared to only 5.6\% under the Give frame, $\chi^2$(1,
N=498)=110.4, p{\textless}.001. Furthermore, the frame also reverses
the relationship between one’s play in the PD and the TOG (Figure 1;
positive interaction between frame [0=Give, 1=Equalize] and TOG choice
[0=Efficient, 1=Equitable] when predicting PD cooperation using
logistic regression: b=2.42, p=.003, see \href{http://journal.sjdm.org/17/171107}{the supplement},
Table S1, for regression details). Under the Equalize frame, subjects
that choose the equitable option are much more likely to cooperate
(49.1\%) in the PD than subjects that choose the efficient option
(22.7\%), $\chi^2$(1, N=250)=19.1, p{\textless}.001. Under the Give
frame, however, the opposite is true (equitable option, 14.5\%C;
efficient option, 36.3\%C; $\chi^2$(1, N=248)=2.8, p=.09).

\renewcommand{\baselinestretch}{1.00} \large\normalsize

\section{Study 2}

Study 2 seeks to replicate Study 1’s result regarding the frame’s effect
on TOG play, and to show that the frame also reverses the relationship
between TOG play and play in a DG where the subject unilaterally
chooses how much of 10 MU to transfer to a passive recipient. Unlike
the PD, beliefs about the other player’s actions have no role in the DG
(since the recipient takes no action). Thus any change in the
relationship between DG and TOG play induced by the frame cannot be
attributed to beliefs. 

\subsection{Subjects}

We recruit N = 379 subjects living in the US at the time of the
experiment on AMT. 

\subsection{Procedure}

% figure 2
\begin{figure}[t]
\includegraphics[clip=true,width=\columnwidth]{fig2.eps}
\caption{Results of Study 2 (N=379): \textbf{Subjects who make the
    nice choice in the Trade-Off Game, whichever that is, give more in
    the Dictator Game.}  We plot average giving in the Dictator Game
  as a function of the choice made in each of the two frames of the
  Trade-Off Game. Error bars represent +/- 1 SEM. Subjects making the
  “nice” choice in the Trade-Off Game, whichever that is, give more in
  the Dictator Game than subjects who make the “non-nice” choice.
  Again, since the nice choice in the Equalize frame is economically
  equivalent to the non-nice choice in the Give frame, this
  correlation cannot be explained by outcome-based preferences and
  suggests that a substantial proportion of DG giving is motivated by
  a preference for “being nice”.}
\end{figure}

Study 2 differs from Study 1 only in that the PD is replaced by a
Dictator game (DG). In the DG, subjects are given \$0.10 and are
asked how much, if any, to give to another subject who is given
nothing. The other subject is given no choice and only gets what
the first subject decides to give.

\subsection{Results}

As in Study 1, TOG play is dramatically altered by the frame in Study
2: under the Equalize frame, 49.2\% of players choose the equitable
option, compared to only 9.3\% under the Give frame, $\chi^2$(1,
N=379)=73.6, p{\textless}.001. And, as with the PD of Study 1, in
Study 2 the frame reverses the relationship between one’s play in the
DG and the TOG (Figure 2; positive interaction between frame [0=Give,
1=Equalize] and TOG choice [0=Efficient, 1=Equitable] when predicting
amount transferred in the DG using linear regression: b=.342,
p{\textless}.001, see \href{http://journal.sjdm.org/17/171107}{SI},
Table S2 for regression details). Under the Equalize frame, subjects
that choose the equitable option transfer substantially more in the DG
(40.1\% of the endowment) than subjects that choose the efficient
option (18.7\% of the endowment), t(183)=6.6, p{\textless}.001. Under
the Give frame, however, the opposite is true (equitable option,
17.2\%; efficient option, 30.0\%; t(192)=2.05, p=.04).

% figure 3
\begin{figure}[t]
\includegraphics[clip=true,width=\columnwidth]{fig3.eps}
\caption{Results of Study 3 (N=263): \textbf{Subjects who make the
    positively framed choice in the Trade-Off Game, whichever that is,
    give more in the Dictator Game.} We plot average giving in the
  Dictator Game as a function of the choice made in each of the two
  frames the Trade-Off game. Error bars represent +/- 1 SEM. Subjects
  making the positively framed choice (more generous or more fair) in
  the Trade-Off Game, whichever that is, give more in the Dictator
  Game than subjects who make the negatively framed choice (less
  generous or less fair, respectively). Thus, the findings from the
  earlier studies generalize beyond the nice vs non-nice framing used
  previously.}
\end{figure}

\section{Study 3}

In Study 3, we investigate whether our results are robust to modifying
the framing of the TOG. Instead of telling subjects that they can
either choose to be nice or not (by choosing either the equitable or
efficient option, depending on condition), in Study 3 we compare a
\textit{Fair} frame (where the equitable option is referred to as “more
fair” and the efficient option “less fair”) with a \textit{Generous}
frame (where the efficient option is referred to as “more generous” and
the equitable option “less generous”). As in Study 2, we pair the TOG
with a DG.

\subsection{Subjects}

We recruit N = 263 subjects living in the US at the time of the
experiment on AMT. 

\subsection{Procedure}

Study 3 differs from Study 2 only in that the frame of the TOG is
modified. In the “give frame”, the equitable choice is termed “less
generous choice” and the efficient choice is termed “more generous
choice”. In the “equalize frame”, the equitable choice is termed “more
fair choice” and the efficient choice is termed “less fair choice”. 

\subsection{Results}

Once again, we see major differences in TOG play based on the frame:
under the Fair frame, 55.3\% of players choose the equitable option,
compared to only 22.9\% under the Generous frame, $\chi^2$(1,
N=263)=29.0, p{\textless}.001. And once again, the frame reverses the
relationship between one’s play in the DG and the TOG (Figure 3;
positive interaction between frame [0=Generous, 1=Fair] and TOG choice
[0=Efficient, 1=Equitable] when predicting amount transferred in the
DG using linear regression: b=.340, p{\textless}.001, see
\href{http://journal.sjdm.org/17/171107}{SI}, Table S3 for regression
details). Under the Fair frame, subjects that choose the equitable
option transfer substantially more in the DG (36.7\% of the endowment)
than subjects that choose the efficient option (18.6\% of the
endowment), t(130)=4.1, p{\textless}.001. Under the Generous frame,
however, the opposite is true (equitable option, 14.3\%; efficient
option, 30.3\%; t(129)=3.05, p=.003).

\section{Study 4}

We would like to argue that these framing effects are the result of
changes in subjects’ perception of which TOG option is the morally
correct choice. To provide more direct evidence for this claim, in
Study 4 we recruit subjects to read the instructions for each game (in
random order), and indicate which option they think is the morally
right choice. 

\subsection{Subjects}

We recruit N=369 subjects living in the US at the time of the experiment
on AMT.

\subsection{Procedure}

Subjects are presented with the rules of the PD, the DG, and the TOG
(both frames), in random order. For each of these games, they are asked
to tell what they think is the morally right thing to do. 

\subsection{Results}

Unsurprisingly, 80.7\% of subjects select cooperation in the PD, and
88.8\% of them select giving half in the DG. Turning to the TOG, the
responses are consistent with our proposal: the frame reverses
subjects’ perceptions of what is morally right, $\chi^2$(1,
N=369)=148.6, p{\textless}.001. Subjects exposed to the Equalize frame
overwhelmingly (76.8\%) rate the equitable option as the morally right
TOG choice, whereas subjects exposed to the Give frame overwhelmingly
(86.4\%) rate the efficient option as the morally right TOG choice.

\section{Study 5}

% figure 4
\begin{figure}[t]
\includegraphics[clip=true,width=\columnwidth]{fig4.eps}
  \caption{Results of Study 5 (N=496): \textbf{Manipulating
      descriptive norm in the Trade-Off Game has virtually no effect
      on the correlation between play in the Trade-Off Game and play
      in the Dictator Game.} We plot average giving in the Dictator
    Game as a function of the choice made in each condition of the
    Trade-Off game (“frame” stands for the framing of the TOG, and
    “norm” stands for the salient norm; for instance, “norm =
    Equitable” means that subjects are informed that we have recorded
    the responses of five subjects who played before them and four of
    them have chosen the equitable option).  Error bars represent +/-
    1 SEM. Subjects making the nice choice in the Trade-Off Game give
    more in the Dictator Game, independently of the frame of the
    Trade-Off Game and independently of the descriptive norm.}
\end{figure}

In Study 5 we recruit subjects to rule out the alternative explanation
that the frame is operating by changing subjects’ perceptions of the
descriptive social norm (i.e., what they think other people would do
(Cialdini \& Trost, 1998)), rather than their perceptions of what is
morally right (i.e., what they think they should do). To do so, we have
subjects again play a TOG and a DG, but this time cross the Equalize
versus Give frame of the TOG with a descriptive social norm
manipulation in which subjects are shown the TOG choices of five
previous subjects. In the Equitable Norm condition, they are shown four
subjects who chose the equitable option and one subject who chose the
efficient option. In the Efficient Norm condition, they are shown four
subjects who chose the efficient option, and one subject who chose the
equitable option. 

\subsection{Subjects}

We recruit N=496 subjects living in the US at the time of the experiment
on AMT.

\subsection{Procedure}

Study 5 implements a 2x2 design in which, after the DG, we manipulate
the framing of the TOG (as in the Studies 1 and 2) and the descriptive
norm. The descriptive norm is manipulated by telling subjects that we
recorded the choices of five subjects who played before them and
only one of them did make or did \textit{not} make the nice choice.

\subsection{Results}

Both in terms of TOG play, and the relationship between play in the
TOG and the DG, we see that the frame has a large effect while the
descriptive social norm information has little effect. In the TOG,
subjects are more likely to choose the equitable option under the
Equalize frame, regardless of the descriptive norm (although the
effect is somewhat weaker under the Efficient Norm condition; logistic
regression shows a significant positive interaction between frame
[0=Give, 1=Equalize] and norm [0=Efficient, 1=Equitable], b=.89,
p=.049, see \href{http://journal.sjdm.org/17/171107}{SI}, Table
S4). With the Equitable Norm, 65.9\% of players choose the equitable
option under the Equalize frame, compared to only 11.7\% under the
Give frame, $\chi^2$(1, N=254)=78.6, p{\textless}.001. With the
Efficient Norm, 53.6\% of subjects choose the equitable option under
the Equalize frame, compared to only 16.2\% under the Give frame,
$\chi^2$(1, N=242)=36.8, p{\textless}.001. See
\href{http://journal.sjdm.org/17/171107}{SI}, Figure S1.

Predicting DG transfer using linear regression, there is a significant
positive interaction between frame [0=Give, 1=Equalize] and TOG choice
[0=Efficient, 1=Equitable] (b=.470, p{\textless}.001), as in the
earlier studies; but no significant interaction between Norm and TOG
choice nor any higher-order interactions (p{\textgreater}.3 for all);
see Figure 4 and \href{http://journal.sjdm.org/17/171107}{SI}, Table
S5. Thus, regardless of the descriptive norm information, it is the
case that under the Equalize frame, subjects who choose the equitable
TOG option give more in the DG than those who choose the efficient
option; and under the Give frame, the opposite is true. Study 5
therefore demonstrates that the effects observed in Studies 1-3 were
not driven by the frame creating an implicit descriptive social norm.

\section{Study 6}

In the previous studies, the choice framed as nice in the TOG – be it
efficient or equitable – is always the active choice, as is the
prosocial action in the DG and in the PD. Thus, it is possible that the
correlation between choosing the nice option in the TOG game and being
prosocial in the PD/DG is driven by a preference for action, rather
than a preference for morality. To rule out this potential alternative
explanation, Study 6 re-explores the correlation between the DG and the
TOG, but this time using a take frame in the DG: now the active choice
in the DG (taking) is selfish, whereas the passive choice (not taking)
is prosocial. Thus, if the results of the previous studies were driven
by preferences for action, then in this study we would see a reversal
of the correlation, such that the prosocial choice in the DG would be
correlated with the non-nice choice in the TOG. Conversely, if, as we
argue, our results were instead driven by preferences for being moral,
then we would find the same pattern as in the previous studies, with
the prosocial choice in the DG being correlated with the nice choice in
the TOG. 

\subsection{Subjects}

We recruit N=275 subjects living in the US at the time of the experiment
on AMT.

\subsection{Procedure}

Subjects are randomly divided in two conditions: the
\textit{DGtake-Equalize} condition and the \textit{DGtake-Give}
condition, similar to those in Study 2. The only difference regards the
instructions of the DG. While in Study 2 subjects played the DG in the
standard “Give frame”, here subjects play the DG in the “Take frame”:
they are told that they are paired with another person and that both of
them start with \$0.05, and that they could take any amount between
0\$0.00 and \$0.05 from the other person. The other person has no choice
and only gets the amount of money unclaimed by the first subject.

% figure 5
\begin{figure}[t]
\includegraphics[clip=true,width=\columnwidth]{fig5.eps}
\caption{Results of Study 6 (N=275): \textbf{Manipulating the active
    choice in the DG has virtually no effect on the correlation
    between play in the Trade-Off Game and play in the Dictator Game.}
  We plot average amount unclaimed in the Dictator Game in the
  “Take-frame” as a function of the choice made in each condition of
  Trade-Off game condition. Error bars represent +/- 1 SEM. Subjects
  making the nice choice in the Trade-Off Game unclaim more in the
  Dictator Game, independently of the frame of the Trade-Off Game.}
\end{figure}

\subsection{Results}

The results are consistent with Study 2. Play in the TOG is
dramatically altered by the frame: under the Equalize frame, 48.2\% of
players choose the equitable option, compared to only 13.9\% under the
Give frame, $\chi^2$(1, N=275)=37.5, p{\textless}.001. And the TOG
frame reverses the relationship between one’s play in the DG and the
TOG in the same way as in Study 2 (Figure 5; significant positive
interaction between Equalize frame and equitable TOG choice when
predicting amount unclaimed in the DG using linear regression: b=.431,
p{\textless}.001, see \href{http://journal.sjdm.org/17/171107}{SI},
Table A6 for regression details).  Under the Equalize frame, subjects
that choose the equitable option leaved more money unclaimed in the DG
(39.6\% of the endowment) compared to subjects that choose the
efficient option (14.2\% of the endowment), t(137)=7.35,
p{\textless}.001. Under the Give frame, however, the opposite is true
(equitable option, 8.9\% unclaimed; efficient option, 26.7\%
unclaimed; t(134)=3.09, p=.001). Thus, these results confirm our
interpretation that the previous findings are driven by preferences
for morality, rather than preferences for action.

\section{Discussion}

Decades of experimental research have shown that people sometimes forgo
personal gains for the benefit of others, and they do so even in
unilateral one-shot anonymous interactions. The standard approach in
behavioral economics to understanding this \textit{pure} prosocial
behavior, which cannot be explained by material self-interest, has been
to assume that people have social preferences for minimizing social
inequities and/or for maximizing social welfare (Bolton \& Ockenfels,
2000; Camerer \& Fehr, 2004; Charness \& Rabin, 2002; Dufwenberg \&
Kirchsteiger, 2004; Engelmann \& Strobel, 2004; Falk \& Fischbacher,
2006; Fehr \& Schmidt, 1999; Rabin, 1993).

Across six experiments, we present results that are inconsistent with
equity or efficient preferences \textit{per se} determining behavior
(and, more generally, with any outcome-based utility function). Instead
of making outcome-based evaluations of all available options, we
observe that prosocial people tend to choose the option that is
presented as being morally right in the given situation, be it
equitable or efficient. We argue that these results support the idea of
a general morality preference.

The idea that people are motivated to be moral is not new. The drive to
appear moral to oneself has received considerable attention in the
psychological literature (e.g., Baron, 2008; Bicchieri, 2005; Jordan,
Mullen \& Murnighan, 2011; Mazar, Amir \& Ariely, 2008; Sachdeva,
Iliev \& Medin, 2009). Several formal models in the economics
literature have incorporated such ideas, as opposed to preferences for
equity or efficiency per se (Alger \& Weibull, 2013; Brekke, Kverndokk,
\& Nyborg, 2003; Huck, Kübler \& Weibull, 2012). Importantly, however,
our results cannot be explained by any of these particular models. For
example, Brekke et al.\ (2003) assume that people are motivated to be
socially responsible and to adhere to their individual “moral ideal”.
On the contrary, again, our results show that the moral ideal is not
individual and can be very easily manipulated. Huck et al.\ (2012)
assume that people choose according to a utility function that is the
sum between their material payoff and a “social payoff”, which, in
turn, is a function of the economic externalities. Thus, the model by
Huck et al.\ (2012) employs an outcome-dependent utility function. On
the contrary, our findings cannot be explained by outcome-dependent
utility functions. Finally, the model by Alger and Weibull (2013)
regards symmetric interactions and thus it does not make clear
predictions in our case. Thus, our results push the boundary of extant
theories of morality preferences. 

Our critique is also distinct from the reciprocity-based argument that
intentions matter as well as outcomes (Dufwenberg \& Kirchsteiger,
2004; Falk \& Fischbacher, 2006; Rabin, 1993), as we largely focus on
unilateral decisions where the other parties take no actions and thus
have no relevant intentions. Our results are also inconsistent with
norms-based preferences where one’s aversion to norm-breaking is
contingent on others also following the norm. For example, López-Pérez
(2008) proposes a model in which people gain utility from choosing
appropriate actions, but this utility is discounted by the extent to
which they expect others to act selfishly and choose inappropriate
actions. They in particular focus on an “E-norm” in which people
determine which actions are appropriate based on some fixed weighting
of equity and efficiency. Neither the E-norm nor their more general
model fit our data, because Study 5 demonstrates that learning that
other people have not chosen the “nice” option has very little effect
on subjects’ behavior: that is, the effects we observe are not
driven by “descriptive norms” (beliefs about the actions of others).
Instead, our experiments demonstrate a causal impact of perceived
morality (an “injunctive norm”) on prosocial behavior.

Prior work on injunctive norms has shown a correlation between an
action’s perceived appropriateness and its likelihood of being chosen
(Krupka \& Weber, 2013). Although these results are consistent with our
general morality preference account, their correlational nature limits
the level of support they can provide. For example, the observed
correlation could be the result of people justifying the action they
want to choose by saying that it is appropriate. Or, both choices and
appropriateness judgements could be driven by other unobserved
variables, including outcome-based preferences that are implemented via
heuristics/bounded rationality (and thus do not perfectly respond to
outcomes, e.g., Capraro, Jordan \& Rand, 2014) or descriptive social
norms (i.e., perceptions of the frequency of others’ actions). Our
experiments, in contrast, \textit{manipulate} the perceived injunctive
norm by varying which option is framed as morally right. We thereby
demonstrate a clear, unambiguous causal effect of perceived morality on
behavior. Even more importantly, we not only examine how average
behavior in a specific game varies as a function of the details of the
setup (as in Krupka and Weber (2013), but also investigate individual
differences in play \textit{across} games. In doing so, we show that
people who cooperate in the PD and give in the DG typically choose the
TOG action which is framed as morally right (be it equitable or
efficient). Thus, we show that a preference for moral action is central
to the basic phenomenon of prosocial behavior in canonical games,
rather than just being important for explaining deviations from
outcome-based preferences in non-standard game setups.

Our morality preference proposal obviously raises the question of what
action is seen as morally right in any given scenario (prior modeling
work has either side-stepped this question entirely and just measured
perceived appropriateness empirically, e.g., Krupka \& Weber, 2013, or
has assumed that judgements of rightness are driven by a fixed
preference for equity versus efficiency, e.g., López-Pérez, 2008, an
assumption which our data show is incorrect). Based on our
experiments, we of course cannot provide an exhaustive
characterization of morality – and, most likely, morality judgments
are driven at least in part by necessarily-imprecise heuristics and
emotions (Capraro et al., 2014; Greene, Sommerville, Nystrom, Darley
\& Cohen, 2001; Haidt, 2001; Rand, 2016).

Finally, our data bear on the debate about the basis of framing effects
in economic games. A long literature has demonstrated that
payoff-irrelevant social frames can alter behavior in economic games.
For example, people cooperate more in a standard PD that is titled the
“Community game” compared to one titled the “Wall Street game”
(Liberman, Samuels \& Ross, 2004). Some have argued that such framing
effects can be accounted for using stable preferences for efficiency
and equity, once you take into account the fact that the frames can
change peoples’ beliefs about the actions of others (Ellingsen,
Johannesson, Mollerstrom \& Munkhammar, 2012). Support for this
position comes from evidence that frames typically have a substantial
effect only in multi-lateral games where there is uncertainty about
other players’ actions, such as the standard simultaneous PD or Public
Goods Game (Dufwenberg, Gächter \& Hennig-Schmidt, 2011; Ellingsen et
al., 2012; Engel \& Rand, 2014; Goerg, Rand \& Walkowitze, 2017;
Liberman et al., 2004), but not in games where there is no uncertainty
about the others actions, such as the asynchronous PD (Ellingsen et
al., 2012) or the DG where the other party takes no action (Chowdhury,
Jeon \& Saha, 2016; Dreber, Ellingsen, Johannesson \& Rand, 2013;
Goerg et al., 2017; Grossman \& Eckel, 2015). Contradicting this
account, however, are the results of Krupka and Weber (2013) who do
find framing effects in a DG, as well as Eriksson, Strimling, Andersson
\& Lindholm (2017) and Larrick \& Blount (1997), who find framing
effects for the second mover in the Ultimatum Game. Our results on
behavior in the TOG, where the frame has a dramatic effect on behavior
despite it being a unilateral decision, provide further evidence that
beliefs alone cannot account for framing effects in economic games.

In sum, we have presented six experiments which demonstrate a causal
effect of perceived morality on prosocial behavior, and show that
responding to this manipulation predicts prosociality in the PD and
DG.  Our results cannot be accounted for by the standard approach to
understanding prosocial behavior in behavioral economics: it cannot be
the case that people’s prosocial behavior is driven \textit{per se} by
preferences regarding inequity and efficiency (or, more generally, any
outcome-based preferences). Instead, the data suggest that people have
a stable preference for doing what they understand to be the morally
right thing in a given situation – a preference which cannot be
cleanly expressed using a purely outcome-based utility function.

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%\vfill
%\break
\end{hangparas}

\bigskip

\section*{Appendix}

\subsection*{The building blocks of our experiments}

Apart from Study 4, all our studies consist of two-stage games. In
general, we will use the notation X-Y to denote the treatment in which
subjects first play game X, then play game Y. For the reader’s
convenience, in this first section, we name each possible X and Y. For
the exact experimental instructions, we refer the reader to Section 2. 

\paragraph{Prisoner’s Dilemma.}
Subjects were given \$0.10 and asked whether they wanted to keep it
(defect) or hand it over to the other subject (cooperate). In the
latter case, the other subject would earn \$0.20. Subjects were
informed that the other subject was facing the same decision
problem.

\paragraph{Dictator Game.}
Subjects were given \$0.10 and asked how much, if any, they wanted
to give to the other person. Subjects were informed that the other
person would have no choice and would only get what they decide to
give.

\paragraph{Dictator Game in the “take frame”.}
Subjects were given \$0.05 and asked how much, if any, they wanted
to take from the other person. Subjects were informed that the
other person would have no choice and would only get the amount they
decide not to take.

\paragraph{Trade-Off Game in the “give frame”.}
Subjects were grouped with other two subjects and asked to
decide between “being nice” and “not being nice”. Being nice means that
the decision maker gets \$0.15, the second player gets \$0.23, and the
third player gets \$0.13; not being nice means that everybody gets
\$0.13.

\paragraph{Trade-Off Game in the “equalize frame”.}
Subjects were grouped with other two subjects and asked to
decide between “being nice” and “not being nice”. Being nice means that
everybody gets \$0.13; not being nice means that the decision-maker
gets \$0.15, the second player gets \$0.23, and the third player gets
\$0.13.

\paragraph{Trade-Off Game in the “give frame (generous)” .}
Subjects were grouped with other two subjects and asked to
decide between “being more generous” and “being less generous”. Being
more generous means that the decision maker gets \$0.15, the second
player gets \$0.23, and the third player gets \$0.13; being less
generous means that everybody gets \$0.13.

\paragraph{Trade-Off Game in the “equalize frame (fair)”.}
Subjects were grouped with other two subjects and asked to
decide between “being more fair” and “being less fair”. Being more fair
means that everybody gets \$0.13; being less fair means that the
decision-maker gets \$0.15, the second player gets \$0.23, and the
third player gets \$0.13.

\subsection*{Experimental instructions}

Here we report full instructions for each of the games we used in our
experiments. The instruction screen started either with “This is the
first part of the HIT” or “This is the second part of the HIT”, etc.,
depending on the order of play. We do not report this part of the
instructions. We do not report the instructions of Study 4, because
they were identical to the instructions of the other studies, with the
only difference that the sentence “What is your choice?” was replaced
with the sentence “What do you think it is the morally right thing to
do?”

\subsubsection*{Prisoner’s Dilemma}

You have been paired with another participant. The amount of money you
can earn depends on your decision and the other
subject's decision. 

You are both given \$0.10 and each of you must decide whether to hand it
over or not. Each time a participant hands over their \$0.10, the other
participant earns \$0.20.

So:

\begin{itemize}\setlength{\itemsep}{-.5ex}
\item If you both decide to hand over the \$0.10, you end the game with
\$0.20
\item If the other participant hands it over and you do not, you end the
game with \$0.30
\item If you hand it over and the other participant does not, you end
the game with \$0
\item If neither of you hand it over, then you end the game with \$0.10
\end{itemize}
Here are some questions to ascertain that you understand the rules.
Remember that you have to answer all of these questions correctly in
order to get the completion code. If you fail any of them, the survey
will automatically end and you will not get any payment.

What choice should YOU make to maximize YOUR gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Hand over
\item Don’t hand over
\end{enumerate}
What choice should YOU make to maximize the OTHER
PARTICIPANT's gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Hand over
\item Don’t hand over
\end{enumerate}
What choice should the OTHER PARTICIPANT make to maximize THEIR gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Hand over
\item Don’t hand over
\end{enumerate}
What choice should the OTHER PARTICIPANT make to maximize YOUR gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Hand over
\item Don’t hand over
\end{enumerate}
Congratulations, you successfully answered all the questions. It is now
time to make your decision.

WHAT IS YOUR CHOICE?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Hand over
\item Don’t hand over
\end{enumerate}

\subsubsection*{Dictator Game}

You have been paired with another participant. The amount of money you
can earn depends only on your choice. You are given \$0.10 and the
other participant is given nothing. You have to decide how much, if
any, to donate to the other participant. The other participant has no
choice and will really accept your donation.

The other participant is REAL and will really get your donation.

Here are some questions to ascertain that you understand the rules.
Remember that you have to answer all of these questions correctly in
order to get the completion code. If you fail any of them, the survey
will automatically end and you will not get any payment.

What is the donation by you that maximizes your bonus?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\item \$0.06
\item \$0.07
\item \$0.08
\item \$0.09
\item \$0.10
\end{enumerate}
What is the donation by you that equalizes your bonus and the other
participant's bonus?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\item \$0.06
\item \$0.07
\item \$0.08
\item \$0.09
\item \$0.10
\end{enumerate}
What amount will you donate to the other person?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\item \$0.06
\item \$0.07
\item \$0.08
\item \$0.09
\item \$0.10
\end{enumerate}

\subsubsection*{Dictator Game in the “take frame”}

You have been paired with another participant. The amount of money you
can earn depends only on your choice. Both you and the other
participant are given 5c. You have to decide how much, if any, to take
from the other participant. The other participant has no choice and
will really get the amount that you decide not to take.

The other participant is REAL and will really get the amount that you
decide not to take.

Here are some questions to ascertain that you understand the rules.
Remember that you have to answer all of these questions correctly in
order to get the completion code. If you fail any of them, the survey
will automatically end and you will not get any payment.

How much should YOU take from the other participant in order to maximise
YOUR gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0.00
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\end{enumerate}
How much should YOU take from the other participant in order to equalise
your and the OTHER PARTICIPANT’s gain?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0.00
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\end{enumerate}
How much will you take from the other participant?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item \$0.00
\item \$0.01
\item \$0.02
\item \$0.03
\item \$0.04
\item \$0.05
\end{enumerate}

\subsubsection*{Trade-Off game in the “give” frame}

You are Player A. You are playing a game with other two players, Player
B and Player C. Each of you starts this game with \$0.13.

You get to make a choice (Player B and Player C do not make
any decisions).

You can either choose to be nice or not. If you choose to be nice, you
earn an additional \$0.02 and Player B earns an additional \$0.10. If
you choose not to be nice, no one earns any additional money and you
all end the game with \$0.13.

This is the only interaction you have with Player B and Player C. They
will not have the opportunity to influence your gain in later parts of
the HIT.

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}
{\bfseries\itshape
Trade-Off game in the “equalize” frame}

You are playing a game with other two players, Player B and Player C.
You start this game with \$0.15, Player B starts with \$0.23 and Player
C with \$0.13.

You get to make a choice (Player B and Player C do not make
any decisions).

You can either choose to be nice or not. If you choose to be nice, you
give up \$0.02 to restore equality, so that you all earn \$0.13. If you
choose not to be nice, no changes are made to the payoffs, and you each
earn what you have started with.

This is the only interaction you have with Player B and Player C. They
will not have the opportunity to influence your gain in later parts of
the HIT.

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}

\subsubsection*{Trade-Off game in the “give (generous)” frame}

You are Player A. You are playing a game with other two players, Player
B and Player C, different from the one you were paired with before.
Each of you starts this game with \$0.13.

You get to make a choice (Player B and Player C do not make
anydecisions).

You can either choose to be more generous or less generous. If you
choose to be more generous, you earn an additional \$0.02 and Player B
earns an additional \$0.10. If you choose to be less generous, no one
earns any additional money and you all end the game with \$0.13.

This is the only interaction you have with Player B and Player C. They
will not have the opportunity to influence your gain in later parts of
the HIT.

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be more generous
\item Be less generous
\end{enumerate}

\subsubsection*{Trade-Off game in the “equalize (fair)” frame}

You are Player A. You are playing a game with other two players, Player
B and Player C. You start this game with \$0.15, Player B starts with
\$0.23 and Player C with \$0.13.

You get to make a choice (Player B and Player C do not make
any decisions).

You can either choose to be more fair or less fair. If you choose to be
more fair, you give up \$0.02 to restore equality, so that you all earn
\$0.13. If you choose to be less fair, no changes are made to the
payoffs, and you each earn what you have started with.

This is the only interaction you have with Player B and Player C. They
will not have the opportunity to influence your gain in later parts of
the HIT.

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be more fair
\item Be less fair
\end{enumerate}

\subsubsection*{Trade-Off game in the “give” frame with the efficient norm}

Instructions were exactly the same as in the “give” frame, a part from
the decision screen that was replaced by:

We have recorded the choices of five players who participated in this
part of the HIT before you:

Previous players choosing to be nice: 4

Previous players choosing NOT to be nice: 1

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}

\subsubsection*{Trade-Off game in the “give” frame with the equitable norm}

Instructions were exactly the same as in the “give” frame, a part from
the decision screen that was replaced by:

We have recorded the choices of five players who participated in this
part of the HIT before you:

Previous players choosing to be nice: 1

Previous players choosing NOT to be nice: 4

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}

\subsubsection*{Trade-Off game in the “equalize” frame with the efficient norm}

Instructions were exactly the same as in the “equalize” frame, a part
from the decision screen that was replaced by:

We have recorded the choices of five players who participated in this
part of the HIT before you:

Previous players choosing to be nice: 1

Previous players choosing NOT to be nice: 4

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}

\subsubsection*{Trade-Off game in the “equalize” frame with the equitable norm}

Instructions were exactly the same as in the “equalize” frame, a part
from the decision screen that was replaced by:

We have recorded the choices of five players who participated in this
part of the HIT before you:

Previous players choosing to be nice: 4

Previous players choosing NOT to be nice: 1

What do you want to do?
\begin{enumerate}\setlength{\itemsep}{-.5ex}\setlength{\itemsep}{-.5ex}
\item Be nice
\item Don’t be nice
\end{enumerate}
\end{document}
