"Twenty pairs of healthy, previously unacquainted male participants participated in the experiment. They were each paid a base $30 fee; each then drew a ball from a hat, labelled ‘rich’ or ‘poor’. The ‘rich’ (high-pay) subject received an immediate payment of $50, whereas the ‘poor’ (low-pay) player received no bonus payment. They then performed an identical task in consecutive fMRI scanning sessions. In each trial subjects viewed possible monetary transfers from the experimenter to themselves and to the other player, ranging from $0 to $50 (Fig. 1). Participants rated how appealing they found the possible transfers on a scale of 25 (very unappealing) to 5 (very appealing). After both players’ scans, a single trial was randomly picked from the set, and the transfers for that trial were paid out." - Tricomi, E., A. Rangel, et al. (2010) Neural evidence for inequality-averse social preferences. 

The above game is an example of what I call an "Act of God" study design, in which researchers (playing God) randomly dole out good and bad fortune to study participants, typically in the form of monetary payments. The researchers then look at the behavior, perceptions or brain activity of the "rich' and "poor" participants to assess the effects of the experimental manipulation, such as evidence that the rich participants whom God favored (got paid more) were uncomfortable with their good fortune. For instance, in the above-referenced study,  brain areas associated with reward lit up in rich participants when they saw poor participants getting more money from the researchers. As if an initial wrong was being put right. Tricomi et al argue these results "provide direct neurobiological evidence in support of the existence of inequality-averse social preferences in the human brain."

Interesting stuff...but I see bias written all over it. First, in the game set-up, labeling the balls "rich" and "poor" in itself primes a social justice mindset. As does the clearly arbitrary allocation of payments. It's not exactly unusual for people who luck out on easy money to grasp that their own good fortune is not exactly fair. And the game is designed so the rich player associates his or her own good fortune with the other player's bad fortune. The researchers basically pushed all the right buttons to make the rich player alert to the unfairness of it all. Is it any wonder that the rich player's brain reward centers lit up when the poor player gets more money later on?

In other words, the study design was rigged to support the inequality-aversion hypothesis. Tricomi et al also discuss their findings in a way that goes way beyond the evidence. For instance, they refer to inequality aversion as a "basic" response and equity concerns as a "pervasive and fundamental feature of human social exchange".  They dismiss issues of deservingness and need as "self-serving biases".  That's a moral judgment masquerading as scientific fact.

What I'd like to see is a study that considers the role of "deservingness" in reactions to inequality, perhaps comparing how subjects respond to unequal allocation of resources when the resources are earned rather than randomly allocated, as has been suggested by Marczyk 2017. It would be easy to control for self-serving biases by making study participants outside observers of resource allocation scenarios involving other people.

Next: What does all this have to do with political agendas?

References:

Marczyk J (2017) Human punishment is not primarily motivated by inequality. PLoS ONE 12(2): e0171298. https://doi.org/10.1371/journal.pone.0171298

Tricomi, E., A. Rangel, et al. (2010) Neural evidence for inequality-averse social preferences.  Nature 463: 1089.