How many levels must an independent variable have in a one-way between groups ANOVA?

A one-way between groups ANOVA is a statistical test used to compare the means of three or more independent (unrelated) groups to determine if there are any statistically significant differences among them. The essence of this type of ANOVA is that the independent variable must have at least three levels because it allows for the comparison of means across these different groups.

If the independent variable had only one level, there would be no group comparisons to conduct. Two levels would allow for a simple t-test to assess differences between just two groups, but the goal of a one-way ANOVA is to analyze situations where there are more than two groups. Therefore, the requirement for three levels or more ensures that the analysis is meaningful, as it can reveal variances that occur across multiple conditions or treatments within the independent variable.