Confidence Interval, Difference between Independent Correlations (1 of 4)
The procedure for computing a confidence interval
on the difference between two independent correlations
is similar to the procedure for computing a confidence interval on one
. The first step is to convert both
values of r to z'
. Then a confidence interval
is constructed based on the general formula
for a confidence interval where the statistic is z'1
, and the standard error of the statistic is:
the number of pairs of scores in r1
number of pairs of scores in r2
. Once the confidence interval
is computed, the upper and lower limits are converted back from z'
to r. As an example, assume a researcher were interested in whether
the correlation between verbal and quantitative SAT scores (VSAT and
QSAT) is different for females than it is for males. Samples of 80
females and 75 males are tested and the correlation for females is
0.55 and the correlation for males is 0.42.