In a courtroom setting, eyewitness testimony tends to be some of the most persuasive to jurors. However, eyewitness testimony is notoriously inaccurate–something most students have learned about in their General Psychology courses. This piece in the Pacific Standard explains a study designed to test how well a new set of instructions to jurors might work. The article begins:
There's a mountain of data cataloguing how bad eyewitnesses are at identifying the people who actually committed a crime. Now, researchers find, one state's attempt to keep the power of dubious testimony in check—essentially, reminding jurors to remain skeptical—works. Actually, it might work a little too well.
The journalist descibes a New Jersey law that requires judges to inform jurors of the fallibility of eyewitness testimony:
…in 2012, New Jersey courts adopted a … solution: Basically, reminding jurors to be extra wary. "Eyewitness identification evidence must be scrutinized carefully," New Jersey judges now instruct juries, reminding them "that human memory is not like a video recording that a witness need only replay to remember what happened." The instructions continue with a crash course in psychology and some examples of the ways our memories can deceive us.
Apparently, some researchers recently conducted an experiment to test how these instructions would work. They recruited over 300 students and had them listen to an eyewitness account. The study was in a factorial design. See if you can decipher the factors and the dependent variable from the journalist's description:
After first watching testimony about a defendant charged with killing a convenience store clerk, then reading either standard jury instructions or the enhanced New Jersey instructions, participants had a simple choice: guilty or not guilty?
At first glance, jury instructions highlighting the messy nature of memory had the intended effect: About one in 10 who got the enhanced instructions voted to convict, compared with one in four of those who heard the standard version.
But stricter scrutiny revealed a lack of nuance in jurors' votes. When the researchers put together the testimony video, they actually made two videos, one emphasizing reasons to trust a witness's memory, and one raising red flags. Theoretically, enhanced instructions should give jurors the tools they need to distinguish strong testimony from weak. In fact, all it did was make them skeptical of eyewitnesses—reading the enhanced New Jersey instructions cut the number of guilty votes roughly in half, regardless of the testimony's strength.
Questions:
a) What are the two independent variables in this experiment? Are the IVs within subjects or independent groups? What is the design? What is the dependent variable?
b) Sketch a line graph or bar graph depicting the results they describe. (Will it matter which IV goes on the x-axis?)
c) Think about the results of the study. Was there a main effect for the first independent variable? Was there a main effect for the second independent variable? Was there an interaction? (hint: the phrase "regardless of the testimony's strength" tells you something about the interaction).
d) What are the practical implications of these results? Assuming that the outcome generalizes to real-world juries, will these instructions lead more innocent people to go free? Or will they lead to more guilty people being exonerated?