Courtroom Biases: "Jury" Decision Making in the U.S. and Sweden

Though the "jury" in most countries that follow the rule of law is expected to be impartial, there are increasing concerns about jury impartiality, especially for minority populations who are likely to face jury pools not of the same minority.

In the U.S., this has been particularly relevant with respect to race, as blacks are disproportionately represented in the criminal justice system but generally constitute a small fraction of the population and (consequently) the jury pool. However, these concerns are by no means unique to the United States.

In Sweden, for instance, which has a jury system that is quite distinct from that of the U.S., there are increasing concerns that criminal defendants, who are disproportionately young and of non-Swedish background, do not receive impartial judgments from Swedish nämndemän (lay judges) who are disproportionately old and politically affiliated.

Empirical evidence of the effects of jury composition

Though extensive, the existing literature on jury biases has a number of limitations, including the methodologies used (primarily mock trials) and its emphasis on juror demographics and the U.S. context. Our previous work provide the first empirical evidence of the effects of jury composition on trial outcomes based on quasi-random variation in jury composition and data from real criminal trials in Florida. The work within the scope of this project fill a number of gaps in the literature:

In the U.S.:

• We study the existence of racial biases in U.S. jury decisions (verdict and sentence) and examine the mechanisms underlying these patterns of impartiality.

• We study how the micro-geography of jurors in the US differs from that of defendants, and the consequences for jury verdicts.

In historical England:

• We study the gender gap in jury decisions over 200 years of trials in England.

• We study the effect of the first female jurors in 1921 on trial verdicts.

• We study the effect of changing punishments (via the abolition of capital punishment) on jury verdicts.

• We study whether the jury’s verdict is affected by the previous cases it saw and decided, i.e. path dependency.

In Sweden:

• We assess whether similar biases exist in the Swedish nämndemän (lay judge) system: do nämndemän political affiliations affect verdicts?

• We open the black box of jury decision making and study how an individul's peers on the "jury" affect his or her vote.

Selected Key Findings

Gender:

• A significant conviction gap favoring females in English trials persists throughout 1700s and 1800s – when all jurors and judges are male.

• Adding females to English juries in 1921 had little effect on overall conviction rates but resulted in a large and significant increase in convictions for sex offenses and on the conviction rate differential between violent crime cases with female versus male victims.

Political Affiliation:

• In Sweden, convictions for young defendants and those with distinctly Arabic sounding names increase substantially when they are randomly assigned jurors from the far-right (nationalist) Swedish Democrat party, while convictions in cases with a female victim increase markedly when they are assigned jurors from the far-left (feminist) Vänster party

Race and geography:

• In Texas, residents from predominantly white and high-income neighborhoods are substantially over-represented in the jury pool. We estimate that Black defendants are more likely to be convicted and receive much longer sentences from juries with a higher share of residents from these over-represented neighborhoods. Simulating outcomes under fair representation implies that the current unequal jury representation increases median sentence length for Black defendants by over 50 percent and more than triples their likelihood of receiving a life sentence when eligible.

Other Biases:

• Decreasing expected punishment (especially via the end of the death penalty), had a large and significant impact on jury behavior, generally leading to the jury being ‘harsher’.

• There is path-dependency in jury decisions: we find that a previous guilty verdict significantly increases the chance of a subsequent guilty verdict (by the same jury) by 6.7-14.1%

Popular Science pieces

Female Representation: Impact of First Female Jurors on Criminal Convictions
VOX CEPR’s Policy Portal, April 19, 2016.

Path Dependency in Jury Decision Making, with Anna Bindler
VOX CEPR’s Policy Portal, September 2, 2018

Jury Verdicts: evidence from eighteenth century London of the dangers of sequential deicison-making, 
Microeconomic Insights, February 25, 2020. 

ProbableCausation Podcast, Episode 31, June 9, 2020

"Tough Love: How Abolishing the Death Penalty Led to More Convictions"
The Economist, April 12, 2017,  

Fitting the punishment to the crime
AEA Research Highlight, November 30, 2018, 

"A Jury Pool’s Race Can Deny Justice"
CNN Opinion Piece, May 23, 2012