ABSTRACT
In Section 65, the calculation of d was illustrated in the examples in which the
two standard deviations were equal. When they are not equal, most researchers divide
the difference between means by the pooled standard deviation, which is a special
type of average standard deviation that can be obtained by using the formula that fol-
lows. Its use is illustrated for an experiment in which the experimental group's stand-
ard deviation is 10.00 (with 15 participants, n = 15), and the control group's standard
deviation is 14.00 (with 12 participants, n = 12). Note that for an experiment, the sub-
script 1 designates the experimental group, and the subscript 2 designates the control
group.