# Normality and ANOVA

## Assess normality when comparing three independent groups on a continuous outcome

The assumption of normality is the first statistical assumption that needs to be tested when comparing three or more independent groups on a continuous outcome with ANOVA. Normality of a continuous distribution is assessed using skewness and kurtosis statistics. In order to meet the statistical assumption of normality, skewness and kurtosis statistics should be below an absolute value of 2.0. If either skewness or a kurtosis statistic is above an absolute value of 2.0, then the continuous distribution is assumed to not be normal. ANOVA should not be conducted on continuous variables that violate the assumption of normality. ANOVA should only be conducted on continuous outcomes that are normally distributed.

### The steps for assessing normality for ANOVA with skewness and kurtosis statistics in SPSS

1. Click

2. Drag the mouse pointer over the

3. Select

4. Click on the outcome variable to highlight it.

5. Click on the

6. Click the

7. Deselect

8. Select the

9. Click

10. Select the

11. Click

**.**__A__nalyze2. Drag the mouse pointer over the

**D**drop-down menu.__e__scriptive Statistics3. Select

**.**__D__escriptives4. Click on the outcome variable to highlight it.

5. Click on the

**arrow**to move the variable into the**box.**__V__ariable(s):6. Click the

**tab.**__O__ptions7. Deselect

**Mi**and__n__imum**Ma**boxes under the__x__imum**Dispersion**section.8. Select the

**and**__K__urtosis**Ske**boxes under the__w__ness**Distribution**section.9. Click

**Continue**.10. Select the

**Save standardi**box.__z__ed values as variables11. Click

**OK**.### The steps for interpreting the SPSS output for skewness and kurtosis statistics when using ANOVA

1. Under the

**skewness**and**kurtosis**columns of the**Descriptive Statistics**table, if the**Statistic is less than an absolute value of 2.0**, then you can assume**normality**of the outcome variable.### Was the assumption of normality met for ANOVA?

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