Scale of Measurement
The first step for choosing a statistical test is to identify the scale of measurement of the dependent variable. All of the parametric tests of means that we have learned to date (e.g., one-sample Z test, one-sample t test, t test for dependent means, t test for independent means) require an interval or ratio scale of measurement.

Many psychologists also apply parametric tests of means to variables with an approximately interval scale of measurement. It is your decision whether to consider approximately interval or "scale" scores as suitable for parametric tests of means.