Parole hearings can have the drama of Shakespearian theater, and in some cases, the stakes are nothing less than the social order and the rule of law. All of this supposedly plays out under the blind eyes of lady justice and her set of scales. But are those eyes truly blind? And are those scales as balanced as they purport to be?

Shai Danziger, a researcher at Ben-Gurion University, sought to answer these questions and more when he tracked the outcomes of more than 10,000 applications for early parole from prison. Danziger’s thesis was simple; he wondered whether parole judges used what he called “extraneous factors” in making their parole decisions.

In his first study, Danziger looked at two obvious extraneous factors, sex and ethnicity. Danziger normalized his data set by ensuring that the severity of the crimes, time served, and the inmate’s behavioral history in prison were all accounted for in his analysis. Reassuringly, his final analysis found no differences in the approval rates of early release based on the sex or ethnicity of the prisoner applying. Roughly two-thirds of all applications, regardless of sex or ethnicity, were approved.

As Danziger considered what extraneous factor to examine next, an old friend mentioned to Danziger that he seemed to get a little grumpier late in the morning right before lunch and then again right before he left for the day. In one of those lightning bolt moments, Danziger was struck with the question of whether some judges’ parole decisions were affected by the time of day. So instead of examining an intrinsic factor of the prisoners themselves, in his second study, Danziger looked at the rates of early release based on the randomly assigned times of the parole hearing.

The results were quite surprising. During the first half of the morning, judges approved three-fourths of parole applications. But in the two hours leading up to the lunch break, the number dropped to two-thirds. And amazingly, when it came to the last case heard immediately before lunch, the approval rate dropped to one in seven. Danziger’s results appeared to show that the time of day had a major impact on whether a prisoner’s application for early release was approved or not.

Danziger believed that the most probable cause of the changes in acceptance rates was the judge’s decreasing blood-sugar level as the morning wore on. Danziger’s theory was that as the judge’s blood-sugar level dropped, the judge would become more critical, where eating lunch restored normal blood-sugar levels. Danziger argued that it was the length of time since the judge last ate that was primarily the culprit.

While Danziger’s landmark study has stood the test of time, his explanation of what he observed has not. His theory would later be challenged by “willpower” researchers at the University of Chicago who believed that the observed phenomenon was caused by something else altogether. These researchers showed conclusively that the determining factor in the decline of approval rates was not blood-sugar levels but rather the number of cases the judge had already heard during that particular court session. The approval rates declined the more cases the judge heard. It didn’t matter if the judge’s first case was at 8 am or 11 am, after hearing four cases, the acceptance rate began to drop. After hearing seven cases, the approval rates plummeted. The researchers argued that the judges expended willpower as they progressed through their docket and when they unconsciously felt they were “running low” on willpower, the judges became hypervigilant and increasingly cautious about which applications they approved.

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