Uploaded March 2022 | Updated September 2026, 10 hours ago

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One of the most common requirements for statistical test procedures is that the data used must be normally distributed. For example, if a t-test or an ANOVA is to be calculated, it must first be tested whether the data or variables are normally distributed. This is done with a test of normality.

If the normal distribution of the data is not given, the above procedures cannot be used and the non-parametric tests, which do not require normal distribution of the data, must be used.

How do I test normal distribution?
Normal distribution can be tested either analytically or graphically. The most common analytical tests to check data for normal distribution are the:
1) Kolmogorov-Smirnov Test
2) Shapiro-Wilk Test
3) Anderson-Darling Test
For the graphical test either a histogram or the Q-Q plot is used. Q-Q stands for Quantile Quantile Plot, it compares the actual observed distribution and the expected theoretical distribution.

Normality test
numiqo.com/tutorial/test-of-normality

Statistics Calculator:
numiqo.com/statistics-calculator/descriptive-statistics