If the variances are relatively equal, that is one sample variance is no larger than twice the size of the other, then you can assume equal variances.
What is the assumption of equal variance?
The assumption of equal variances (i.e. assumption of homoscedasticity) assumes that different samples have the same variance, even if they came from different populations. The assumption is found in many statistical tests, including Analysis of Variance (ANOVA) and Student's T-Test.
How do you know if equal variances assumption is met?
There are two ways to test if this assumption is met:
- Use the rule of thumb ratio. As a rule of thumb, if the ratio of the larger variance to the smaller variance is less than 4, then we can assume the variances are approximately equal and use the two sample t-test. ...
- Perform an F-test.
