Measuring interjudge sentencing disparity: Before and after the federal sentencing guidelines

This paper evaluates the impact of the Federal Sentencing Guidelines on int erjudge sentencing disparity, which is defined as the differences in averag e nominal prison sentence lengths for comparable caseloads assigned to diff erent judges. This disparity is measured as the dispersion of a random effe ct in a zero-inflated negative binomial model. The results show that the ex pected difference between two typical judges in the average sentence length was about 17 percent (or 4.9 months) in 1986-87 prior to the Guidelines an d fell to about 11 percent (or 3.9 months) in 1988-93 during the early year s of the Guidelines. We have not sought to measure the effect of parole in the pre-Guidelines period, other sources of disparity such as prosecutorial discretion, or the proportionality of punishment under the Guidelines as c ompared with the pre-Guidelines era.