To use a parametric test the 3 characteristics below must be satisfied:
Data must be interval, because parametric tests use the actual score, rather than ranked data
Data should be drawn from a population where a normal distribution for the variable being measured (DV) is assumed, e.g. time, weight, temperature.
There should be homogeneity of variance – the set of scores in each condition should have a similar spread (generally assumed to be similar in related design but can check this by comparing the standard deviations).)
