The Impact of Joinder and Severance on Federal Criminal Cases: An Empirical Study

It is widely assumed that criminal defendants who face multiple charges in a single trial have a harder time prevailing than those who face several trials of one count each. Conventional wisdom also has it that a defendant who is joined for trial with other suspects is worse off than one who stands trial alone. Until now, these assumptions have never been tested empirically. Looking at nearly 20,000 federal criminal trials over a five-year period, this Article asks if the traditional beliefs are true, and if so, tries to measure the impact on trial outcomes of joining counts and defendants. It turns out that joinder has a significant prejudicial effect on trials, although not quite the same effect that is usually assumed. Using statistical models that control for a range of variables, the authors discovered that trial defendants who face multiple counts are roughly 10% more likely to be convicted of the most serious charge than a defendant who stands trial on a single count. Surprisingly, however, joining co-defendants in a single trial had virtually no impact on the likelihood of conviction, at least in the aggregate. Using the results of the empirical study, the Article then reconsiders the competing policy issues that underlie the joinder and severance doctrine, and explores the implications of the findings. I. INTRODUCTION Dave is in trouble. It was bad enough to be arrested for bank robbery; now he has learned that the prosecutor plans to join the current charge with three other, unrelated bank robberies and present all four counts in a single trial. To his priest and to his lawyer, Dave admits that he committed the first and the second robberies, but he did not commit the third or fourth. Dave is smart enough to realize, however, that once the jury starts hearing evidence of some of the crimes-all of which will sound quite similar-his ability to cast doubt on the remaining charges will be dimmed. And Dave's lawyer is smart enough to know that once the charges are joined, the chances of splitting them apart are relatively small. It is widely assumed that criminal defendants who face multiple charges in a single trial have a harder time prevailing than those who face several trials of one count each. Conventional wisdom also has it that a defendant who is joined for trial with other suspects is in a worse position than one who stands trial alone. These assumptions have never been tested empirically; this Article tries to fill the gap. Looking at nearly 20,000 federal criminal trials over a five-year period, the Article asks if the traditional beliefs are true and, if so, tries to measure the impact on trial outcomes of joining counts and defendants. The effect of joinder on criminal cases is part of a larger debate about how best to manage a growing criminal docket while still providing individual justice. The battle lines are easy to describe: courts and prosecutors typically want joined proceedings, defendants usually don't. Courts believe that consolidated proceedings play a "vital role"1 in the administration of justice; defendants believe that they are a source of great prejudice. The problem is that both sides are right. The details of joinder and severance law are dry, even boring, and perhaps as a result, the impact of consolidated trials has received little scholarly attention.2 But the consequences are widespread: more than half of all federal defendants are charged with multiple counts, roughly one-third are joined with other defendants, and an overlapping one-quarter face both-a single proceeding with multiple charges plus one or more co-defendants.3 If joinder makes a conviction significantly more likely, it should have a bearing on prosecutors' charging decisions, judicial rulings on severance motions, and defense decisions on whether to plead or stand trial. More importantly, understanding the dimensions of any prejudice should tell us something important about the tradeoffs we make between fairness to the accused and efficiency in processing criminal cases. …