Dateline: January, 2009, Issue 2
Sometimes defendants are tried simultaneously for multiple crimes.
Tanford (Tanford, 1985; Tanford & Penrod, 1984) studied the effects of trying a defendant on three charges in one trial, or trying the defendant separately on each charge.
Defendants were more likely to be convicted when tried on multiple charges, than on the same charge tried by itself.
The order of presentation of the charges also mattered. Defendants facing three charges were more likely to be convicted of a charge presented in the third position.
Jurors judging trials involving multiple, rather than separate charges, also confused evidence among charges, thought the prosecution's evidence was stronger, and perceived the defendant less favorably than jurors judging trials on each charge separately.
Being tried on just two charges is also enough to increase convictions when compared to being tried on each charge separately. Greene and Loftus (1985) found that a defendant charged with two charges (rape and murder) was more likely to be found guilty of at least one charge, than when the defendant only faced one charge (rape or murder). The defendant was perceived in a more negative way when standing trial on two offenses. The order in which the charges were heard had no effect, nor did instructions to jurors to judge the charges separately.
One charge supported with much stronger evidence than the other charge makes acquittal on the weaker charge more likely. Kerr and Sawyers (1979) found that as the strength of evidence on one charge increased, the probability of conviction on the other charge decreased.
Trials involving multiple charges increase convictions. As evidence grows stronger on one charge, acquittal is more likely on other charges.
Source Tanford, S. (1985). Decision-making processes in joined criminal trials. Criminal Justice & Behavior, 12, pp. 367-385.
Source Tanford, S. & Penrod, S. (1984). Social inference processes in juror judgments of multiple-offense trials. Journal of Personality and Social Psychology, 47, pp. 749-765.
Source Greene, E. & Loftus, E. F. (1985). When crimes are joined at trial. Law and Human Behavior, 9, pp. 193-207.
Source Kerr, N. L. & Sawyers, G. W. (1979). Independence of multiple verdicts within a trial by mock jurors. Representative Research in Social Psychology, 10, pp. 16-27.