Matching effort to ensure fairness

– by Marcell Székely & John Michael

Imagine that you and your neighbor collaborate to clear away weeds from the common garden where strawberries grow. Assuming you and your neighbor spend about the same amount of time weeding, a reasonable expectation is that you would divide up the strawberries equally.  In contrast, if your neighbor has spent more time weeding than you have, you might think it reasonable that they should receive a greater share of the strawberries. Or if your neighbor spends less time than you weeding, you might think it reasonable to expect more strawberries for yourself.

This everyday example illustrates that we have a sense of fairness, which leads us to divide rewards of joint actions equitably among contributors. Moreover, it shows that this sense of fairness is not just a blind tendency to divide rewards equally but that it takes effort contributions into account. And indeed, recent research has confirmed that our intuitions about this hypothetical scenario are reflected in people’s actual behavior in controlled scenarios. For example, Frohlich and colleagues found that when participants were placed in one room and had to proofread a text to correct spelling errors for joint rewards, they divided their collectively earned rewards in proportional to individual effort costs. Even more strikingly, recent studies in developmental psychology have even shown that three-year-old children take effort costs into account to achieve a fair distribution of rewards. For example, Kanngiesser and Warneken found that three-year-old children kept more stickers after working more than their partner.

But now let’s tweak our hypothetical example: imagine that you and your neighbor partner are tidying up the stairwell together. Notice that in this version of the hypothetical scenario, there is no tangible reward that could be divided up at the end, so fairness cannot be assured through the division of rewards. So what would you do if you perceived that your neighbor was investing a higher level of effort than you? Or a lower level of effort?

In a new article, we describe a series of experiments which we conducted to investigate how people deal with such scenarios. In the experiments, we adapted an effort discounting task developed by Hartmann and colleagues. In the adapted paradigm, people are asked to make decisions about how much effort to invest (namely, by spending time pressing the spacebar repeatedly) for different monetary rewards. This makes it possible to quantify the costs people associate with different levels of effort and to investigate how people trade off those costs against monetary reward.

We turned this paradigm into a social task by letting participants observe their partner performing an effortful cognitive task in order to ‘unlock’ the effort discounting task. Previous research has shown that people spontaneously track others’ ongoing effort investments, and indeed do so accurately. Moreover, we were confident that participants would track the partner’s effort investment using these stimuli because this effort perception manipulation was successfully used in Székely and Michael and Chennells and Michael. Sometimes, participants were rewarded jointly, sometimes they were rewarded separately. This enabled us to test whether participants chose to invest different degrees of effort against monetary reward based on their relationship to the other person. In other words, it enabled us to investigate how social context modulates people’s decisions about how much effort different rewards are ‘worth.’

Our main finding was that people invested more effort when they were rewarded jointly with their partner than when they were rewarded separately. This provides evidence that when rewards cannot be divided to ensure fairness, people instead boost their effort investment as a means of ensuring fairness with a cooperation partner. In other words, the sense of fairness governs not only the distribution of rewards but the allocation of effort in joint actions.

This is important because, while most research on the evolution of the sense of fairness has focused on the division of rewards, a great many cooperative endeavors now, as in deep evolutionary history, do not produce any distributable rewards at all. One reason for this is that the success of cooperative endeavors is always at least to some extent uncertain. Like individual endeavors, they may not succeed because of exogenous factors or lack of competence. In addition, they may not succeed because the collaborative partner may encounter a tempting outside option and so may prematurely withdraw from the joint activity. For example, hunting and foraging in ancestral environments were uncertain endeavors, and they may not have yielded any rewards to distribute at all. Moreover, even if a joint activity yields a reward, this reward may not be divisible. For example, tidying up the stairwell or building a shelter together may not produce any divisible rewards. In such activities, there is nothing to distribute at the end, but it is still possible to distribute the effort costs. This may explain why our participants were willing to invest more effort in a joint action, and thereby to increase the potential rewards for themselves and their partner, when their partners had apparently invested a high degree of effort, even if the partner’s effort investment did not increase the potential rewards.

These findings also open up important new avenues of research on the evolution of cooperation: most of the empirical studies investigating the evolutionary origins and motivational mechanisms to cooperate have focused on the exchange of money, and their results are commonly used to support claims about humans’ willingness and motivation to cooperate more generally. While this focus on monetary rewards is justifiable, people often have to make decisions about how to divide up other resources as well as costs in the context of cooperative endeavors – and had to do so in our deep evolutionary past. It is therefore crucially important to extend the scope of our focus to resources other than monetary rewards. The current findings are an invitation to take up this important challenge.

The findings also provide new impulses for future research about whether and how the sense of fairness may be sensitive to specific features of cooperation partners, such as their competence. While we intentionally bracketed out questions about the relative competence of different actors for our study, parties to cooperative endeavors often contribute with different levels of competence. We look forward to the results of future research investigating how this is reflected in people’s decisions about the distribution of rewards and allocation of effort costs.

Read the original article: Székely, M., & Michael, J. (2023). In it together: evidence of a preference for the fair distribution of effort in joint action. Evolution & Human Behavior, 44(4), 339-348.