I have a question about Scoring the IAT. I have an finished SPSS File with the IAT Reactionstime (One Line Per Subject) with the variables compatibleblock and incopatibleblock...
I calculated an IAT Score by just using the mean difference over subjects between the two blocks...
Can somebody tell me how I can calculate the D-Score out of it? What exactly is the advantage of the D-Score in contrast to the plain difference between the two blocks?
Can you also tell me which correlation coefficient you use for correlations with explicit measures?
Thanks a lot
All of this is discussed at length in Greenwald et al. (2003), available here: http://faculty.washington.edu/agg/pdf/GN&B.JPSP.2003.pdf. Additionally, SPSS syntax for computing D-scores from data gathered with IAT Inquisit templates is available from the IAT download page: http://www.millisecond.com/download/samples/v3/IAT/default.aspx.
The appropriate correlation coefficient would depend on a number of factors (design, scale level, etc.). Pearson's r should be okay to use in most cases. However, I suggest you look through the available research literature, find a similar case to yours and check what was used there.
Thanks for your quick answer. OK I found something in the stuff you told me for inspection. This is kind of a manual how to calculate the D-Score.
COMPUTE Numerator_for_D = (Mn2 - Mn1) .
COMPUTE Denominator_for_D = SQRT( ( ((N1-1) * SD1**2 + (N2-1) * SD2**2)
+ ((N1+N2) * ((Mn2-Mn1)**2) / 4) ) / (N1 + N2 - 1) ) .
COMPUTE D = Numerator_for_D / Denominator_for_D .
And I also don't understand what the double **means...
Since trials with latencies greater than 10.000ms are to be discarded according to Greenwald et al.'s "improved scoring algorithm", N1 and N2 aren't necessarily equal.
Exponentiation, more commonly denoted as a^n.