Role of Sample Size - Precision
confidence interval represents the precision with which we are able to
report the effect size, and the larger the sample, the more precise the
estimate. As a practical matter, sample size is often the dominant factor
in determining the precision.
Note: For studies that involve two groups precision is maximized when the subjects are divided evenly between the two groups (this statement applies to the procedures included in this program). When the number of cases in the two groups is uneven the "effective N" for computing precision falls much closer to the smaller sample size than the larger one.