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In addition, these data are combined into the discrimination index referred to as A’ (A-prime) where

Rates are computed as the proportion of judgments that fall into each of the response categories. The resulting number A’ ranges from .50, mere chance discrimination, to 1.00, perfect discrimination. (For information on A’ and other indices of discrimination, see a standard sensation and perception text such as Coren, Porac, & Ward.). In summary, then, five pieces of data are stored for each participant who completes the Day 1 portion of the experiment: Number of Hits, Misses, False Alarms, Correct Rejections, and then the derived measure A’.

When participants return to the Facial Recognition Experiment on Day 2, the program retrieves the list variables that specify which faces were assigned to which list (Most Wanted, Foils List1, and Foils List 2). Based on these, a new Mug Book identification task is constructed. As before, there are 20 serially presented faces. Ten are the Most Wanted faces and the other 10 either Foils List 1 or Foils List 2. The choice is made randomly based on whether the minutes on the system clock is odd or even.

Using two different Mug Books on Day 2 creates a between subject variable for analysis. Research participants who get a Day 2 Mug Book that includes the original Most Wanted faces and 10 previously unseen foils are control subjects. Their performance decline from Day 1 to Day 2 will reflect the effect of time alone on the memory for the Most Wanted faces. But the memories of subjects who get a Day 2 Mug Book that includes the same 20 faces as the original Day 1 Mug Book will be affected by more than just time. Their memories will be affected also by the intrusion of false recognitions that result from seeing a "familiar" face. For that reason, this study of facial recognition is really a study in false recognition: To what extent does seeing a distractor face in the same temporal context as a to-be-remembered face increase the probability that the distractor face will later be falsely identified as one of the to-be-remembered faces?
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One way to address this question statistically is to compare the discrimination index scores for participants in the Control and False Recognition groups. Discrimination index scores are good because they combine information from the four specific measures–Hits, Misses, False Alarms, and Correct Rejections. But it would also be of interest to examine false alarm rates in the two groups because this is a direct measure of the effect that repeating foils should have.

The data to the left show the results of a false recognition study conducted at UM in Fall 1998. The dependent variable in this case is the discrimination index A’. The raw data are given in the table below along with summary statistics.

The data obtained via the Download data link on the PsychExperiments homepage are comma delimited.  The first entry (up to the first comma) is the affiliation of the research participant.  Typically this is the class to which the participant belongs.  Non-affiliated participants use the default entry of Interested Person. Next is the randomly assigned ID code for the research participant. The third and fourth entries are the data and time (24-hour format) on the server when the data were received.  Because no data is collected on subject variables in this experiment, raw data come next.  The data consist of 2 "trials," which for the Facial Recognition study are just dummy entries that are required by the generic format used for data at PsychExperiments. Following these dummy entries is an explicit entry for Day1 or Day2. Next are entries for the date and time of the data entry (which is included so that instructors can verify that students did in fact collect their data 24 hours apart). Ignore the 1/1/1900 entry prior to the time as irrelevant.  Next comes an explicit record of the experimental condition to which the participant was assigned--False Memory or Control. Next is an entry for the FoilsList that was used for the research participant.  This information is redundant with the Condition assignment because when the Foils List values match for Day1 and Day2 the participant was in the False Memory Condition. When they do not match, the subject was in the Control condition. Next come the actual performance data.  They are number of hits, number of misses, number of false alarms, number of correct rejections, and then the Discrimination Index A' (described above).  

The table below gives the data format (excluding user information) The text line below that shows a complete data set for one research participant.