Hello all,
I have been reviewing the IAT SPSS
command syntax for processing IAT data which I downloaded here (
http://www.millisecond.com/download/library/IAT/ ). I have also been reviewing the Greenwald, Nosek, and Banaji (2003) article which outlines the syntax. Greenwald, Nosek, and Banaji (2003) state that the only difference between Cohen's d and D is that the standard deviation in the denominator of D is calculated from the scores in both conditions, ignoring condition membership. The denominator for D appears in the command as following
D_asis_denom = SQRT( ( ((N1-1) * SD1**2 + (N2-1) * SD2**2) + ((N1+N2) * ((M1-M2)**2) / 4) ) / (N1 + N2 - 1) )
The denominator for Cohen's d (pooled within treatment standard deviation), in the same format, i believe is
SQRT( ((N1-1) * SD1**2 + (N2-1) * SD2**2) / (N1 + N2 - 2) )
I do not understand how the differences between these two denominators can be simply explained by D ignoring condition membership, while d does not.
Does including the addition of ((N1+N2) * ((M1-M2)**2) / 4) and subtracting by 1 instead of 2 somehow account for ignoring condition membership? I have scoured the forums and other articles by Greenwald, Nosek, and Banaji for an explanation, but can not find one.
Thanks in advance for the help! I am so grateful for all the information the forums have already provided.