What are parametric and non-parametric criteria, and when are they used?

Parametric criteria are statistical methods that assume data follow a specific distribution (usually normal). They use parameters of this distribution (e.g., mean and variance) to test hypotheses. Examples: t-test, ANOVA.

Non-parametric criteria do not make assumptions about the data distribution. They are used when data do not meet parametric requirements or when data are ordinal or categorical. Examples: Mann-Whitney test, sign test.

When to use:

• Parametric — if data are normally distributed and the sample size is sufficient.
• Non-parametric — if data are not normal, the sample is small, or data are not quantitative.

This is important for choosing the correct analysis method and obtaining reliable results.