Why are unequal sample sizes a problem?
Unequal sample sizes can lead to: Unequal variances between samples, which affects the assumption of equal variances in tests like ANOVA. Having both unequal sample sizes and variances dramatically affects statistical power and Type I error rates (Rusticus & Lovato, 2014). A general loss of power.
What is Welch’s t-test used for?
The Welch t-test is an adaptation of Student’s t-test. It is used to compare the means of two groups of samples when the variances are different.
Should you always use Welch’s t-test?
In practice, when you are comparing the means of two groups it’s unlikely that the standard deviations for each group will be identical. This makes it a good idea to just always use Welch’s t-test, so that you don’t have to make any assumptions about equal variances.
What is unequal variance t-test?
For the unequal variance t test, the null hypothesis is that the two population means are the same but the two population variances may differ. The unequal variance t test reports a confidence interval for the difference between two means that is usable even if the standard deviations differ.
Can you do a paired t-test with unequal sample sizes?
All Answers (13) Hey Luke. A paired t-test when you have unequal sample sizes does not make any sense, conceptually or mathematically. Conceptually, a paired t-test is good for when your “before” values have a lot of variance, relative to the difference between your before and after values.
What does it mean to have unequal variances?
The conservative choice is to use the “Unequal Variances” column, meaning that the data sets are not pooled. This doesn’t require you to make assumptions that you can’t really be sure of, and it almost never makes much of a change in your results.
Which t-test is equal or unequal variance?
Welch’s t-test: Assumes that both groups of data are sampled from populations that follow a normal distribution, but it does not assume that those two populations have the same variance. So, if the two samples do not have equal variance then it’s best to use the Welch’s t-test.
What does unequal variance mean?
Is Chi-square a statistical test?
Chi-square is a statistical test used to examine the differences between categorical variables from a random sample in order to judge goodness of fit between expected and observed results.
Why is ANOVA used instead of t tests?
The Student’s t test is used to compare the means between two groups, whereas ANOVA is used to compare the means among three or more groups. A significant P value of the ANOVA test indicates for at least one pair, between which the mean difference was statistically significant.