Cross Validated is a question and answer site for people interested in statistics, machine learning, data analysis, data mining, and data visualization. It only takes a minute to sign up.
Sign up to join this community
I'm trying to compare mean interest levels of 3 products. The same sample was asked about each of the three products. How can I test for equal means among the three products?
Other information: Interest level was quantified using Likert scale. Sample size is 200.
In order to compare multiple means within the same subjects you can use 'paired' analyses. In case of two means, you can choose to use a paired t-test. In case of 3 or more means, you could use a paired version of an ANOVA: repeated measures ANOVA with a within-subject factor (product).
However, it is important to note that these kinds of analyses assume a normally distributed, continuous outcome. Your outcome has an ordinal distribution, so it could be that another analytical method would be a better fit. One option is to use a non-parametric test for paired data that does not assume normality, e.g., Wilcoxon signed-rank test. Another option is to use a form of ordinal regression that takes into account the nested structure of the data. Here, you could for instance consider Generalized Estimating Equations.
