Unpaired

Interval

Large sample

Z (NORMAL DISTRIBUTION) TEST FOR THE COMPARISON OF MEANS: This is listed in the parametric methods section of the analysis menu. With large samples we can assume that the means are normally distributed and that the variances are good estimates of their population values. The definition of a large sample is somewhat debateable but > 100 is a reasonably safe level. You will find some authors quoting > 50 and even > 30 as large samples but StatsDirect favours a more conservative approach.