What does "k" represent in statistical notation?

In statistical notation, "k" is commonly used to represent the number of levels or groups in a factor as well as the number of categories in categorical data. Hence, in the context of the question, the correct interpretation points to "k" as the number of factor levels. Factorial designs in experiments often utilize "k" to denote the different conditions or groups that are being compared.

Understanding the role of "k" is essential because it helps in determining how many groups are analyzed within a sample, which can influence various analyses such as ANOVA, where distinguishing between multiple levels of a factor is crucial. Proper identification of factor levels guides the choice of statistical methods and interpretation of the results.