The three studies show considerable overlap in technique. For example, the presence versus the absence of expert psychological testimony was manipulated as an independent variable with, overall, the similarities and differences among the three studies providing optimal information about the reliability and generalizability of the obtained effect. All three investigations obtained significant influences on jurors as a function of expert testimony. The presence of expert testimony caused jurors to increase their scrutiny of the evidence and to decrease their beliefs in the general accuracy of eyewitness testimony. Expert testimony accounted for 3 percent of the variance in verdicts and 68 percent of the variance in the time jurors deliberated about eyewitness testimony. Overall, expert psychological testimony benefits the courts by increasing jurors' consideration of case evidence. Nevertheless, psychological experts must be aware of their purpose for testifying -- to provide the triers of fact with information that is firmly ground in empirical data -- and should not relate their information to the accuracy of a particular eyewitness. A table and 11 references are provided. (Author abstract modified)