Explanation of Variables in the Effect Size Statistic.
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Mean Gain:
1. Effect size = the mean at time 2 -- the mean at time 1.
is the pooled variance. "s" represents the variance at time 1 and time 2. For the pooled standard deviation, take the square root of both sides.
2. n = the common sample size at time 1 and time 2.
3. r = the correlation between time 1 and time 2 scores (this value can be found in a table)
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Mean Difference:
Refers to the mean for group 1, while refers to the mean for group 2.
is the number of subjects (the subscript specifices if it is for group 1 or 2).
The standardized equations call for ES prime, calculated using this equation, to correct for small sample size bias. Use this corrected equation to calculate ES, SE, and w.
N = the total sample size (n from group 1 + n from group 2).
See the Mean Gain section for further explanation of pooled variance.
