Method

Given the substantial overlap in methods across all four studies, we describe all four studies concurrently. All studies conducted for this project are reported, as are all experimental manipulations, and all measures pertinent to our central research question.1

To our knowledge, the only correlational study examining the relationship between dispositional belief in free will and prosocial or antisocial behavior is Study 2 of Baumeister, Masicampo, and Dewall (2009) ; all other studies of FWBs and moral behavior are experimental in nature (relying on undermining or boosting people’s FWBs rather than measuring preexisting beliefs). In the Baumeister et al. study, the authors observed a significant, positive association between FWBs and helping behavior (β = .30). Across all four studies, we achieved 80% power to detect correlations between .16 (Study 3) and .20 (Study 4), and in the pooled data analysis reported in the Supplementary Material (combining data from Studies 2 to 4), we had 80% power to detect a correlation of .10 (assuming any such effect is unrelated to the subtle methodological differences across studies).

Participants were excluded if they either provided incomplete data or failed attention checks. In Studies 1–3, which included multiple attention checks, participants were excluded for failing more than one attention check. Because Study 4 had only one attention check, all participants failing this attention check were excluded. The number of people excluded per study is summarized in Table 2 .

For all studies, participants were recruited via Amazon’s Mechanical Turk. Eligibility was restricted to workers located in the United States with approval rates ≥95%, and ≥1,000 previously approved jobs. A summary of demographic information for each study is provided in Table 1 .

Materials and Procedure

The specific measures used in each study are summarized in Table 3. In all studies, we administered measures of FWBs, prosocial behavior, and moral identity. In Studies 2–4, we also included a measure of antisocial behavior. Additionally, Studies 2 and 3 included a measure of social desirability, and Study 4 included an unsuccessful FWB manipulation. These are both described further in the Supplementary Material.

Table 3. Summary of Key Measures.

FWB measures In all four studies, participants completed the FAD-Plus (Paulhus & Carey, 2011). The FAD-Plus is a 27-item self-report measure of belief in free will in which participants rate the extent to which they agree with each statement on a scale from 1 (strongly disagree) to 7 (strongly agree) with the statements forming four subscales: Free Will (e.g., “People have complete free will”), Scientific Determinism (e.g., “Your genes determine your future”), Fatalistic Determinism (e.g., “I believe that the future has already been determined by fate”), and Unpredictability (e.g., “People’s futures cannot be predicted”). In Study 4, participants only completed the Free Will subscale. In Studies 1–3, participants also completed the Free Will Inventory (FWI; Nadelhoffer, Shepard, Nahmias, Sripada, & Ross, 2014). The FWI is a 29-item self-report measure of belief in free will, divided into two parts. In the first part (15 items), participants rated the extent to which they agree with each statement on a scale from 1 (strongly disagree) to 7 (strongly agree) with the statements forming three 5-item subscales: Free Will (e.g., “People always have the ability to do otherwise”), Determinism (e.g., “Given the way things were at the Big Bang, there is only one way for everything to happen in the universe after that”), and Dualism and Nonreductionism (e.g., “Each person has a nonphysical essence that makes that person unique”). In the second part (14 items), using the same 7-point scale, participants report the extent of their agreement with individual statements regarding the relationships between free will, determinism, choice, the soul, predictability, responsibility, and punishment. As these items are not intended to form composite scales, we present analyses of each individual item in the Supplementary Material. Both the FAD-Plus and FWI have undergone factor-analytic validation in multiple studies and samples (Nadelhoffer et al., 2014; Paulhus & Carey, 2011), and as shown in Table 3, both measures of FWBs were highly reliable (all αs ≥ .85 across all studies). Moreover, both measures were strongly correlated with each other (rs = .85, .82, and .76) across Studies 1–3.

Measures of prosocial behavior In Study 1, participants completed a charity dictator game (DG). In the DG, participants were endowed with a 10-cent bonus (i.e., an additional 12.5% on top of their base payment) and given the opportunity to donate some or all of it to the American Red Cross. For Study 2, we made multiple changes to our operationalization of prosocial behavior. First, given the substantial floor effect on generosity in Study 1 (48% of participants donated nothing), we sought to increase the value participants placed on the recipient by providing a choice between four different charities to nominate as the beneficiary in their allocation decisions, instead of having all donations directed to one charity.2 Second, instead of using a single DG allocation, we attempted to obtain a more sensitive measure of prosocial inclinations by using the social value orientation (SVO) slider measure (Murphy & Ackermann, 2014; Murphy, Ackermann, & Handgraaf, 2011). This measure entails a series of allocation decisions (much like mini DGs) that can be used to measure the weight one places on one’s own versus other’s interests.3 For each item, participants chose one of nine possible allocations with differing payoff structures. Participants distributed points between themselves and their nominated charity at an exchange rate that was described before participants began making their allocation decisions. These points were subsequently converted into money and paid out to both parties according to the participants’ decisions. For Studies 3 and 4, we used the SVO slider measure again, but instead of allowing all participants to allocate a small amount of money, we increased the payoffs and instituted a lottery-based system where only a single randomly selected winner would have their allocations realized in each study. In Study 2 (where all participants were paid according to their choices), the exchange rate was 10 points to one cent. In Studies 3 and 4 (which employed lotteries), the exchange rate was one point to five cents (see Table 3 for further details). SVO angles were calculated using the MATLAB analysis scripts described in Murphy, Ackermann, and Handgraaf (2011).

Measures of antisocial behavior To provide a complementary measure of moral behavior, Studies 2–4 also included a dice cheating task (Fischbacher & Föllmi-Heusi, 2013; Suri, Goldstein, & Mason, 2011), in which participants had the opportunity to lie without detection to earn a bonus. Specifically, participants were informed that they would roll a die, which would be used to determine the size of a bonus that they would receive. Participants were instructed to roll a die (either an actual one, or an online one, hosted on an independent website, whichever they preferred), privately record the number they rolled, and then proceed to the next page of the survey where they simultaneously (1) learned which numbers corresponded to which bonus size4 and (2) were given the opportunity to report the number they rolled. The fact that we could not observe any participant’s die roll made it possible for participants to lie to inflate the size of their bonus (e.g., rolling a one but reporting a five). Crucially, however, because of the known (i.e., uniform) distribution of dice rolls, it was possible to detect the presence of cheating at the group level and to link this to individual difference variables (e.g., to see whether people who disbelieve in free will are “luckier”). Similar to the measures of prosocial behavior, the payoffs in Study 2 were low but certain, and the payoffs in Studies 3 and 4 were substantially higher but realized for only one randomly selected participant per study (see Table 3 for further details).