American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Friedman's ANOVA is appropriate for which type of data?

1. Skewed data

2. Ordinal data

3. Normal data

4. Nominal data

The correct answer is: Ordinal data

Friedman's ANOVA is particularly suitable for analysis of ordinal data. This non-parametric statistical test is used to detect differences in treatments across multiple test attempts by analyzing ranked data rather than raw values. When the data is ordinal, it implies that the values represent an ordered relationship, allowing for the ranking essential for this method. Since Friedman's ANOVA deals with repeated measures on the same subjects, it is ideal for situations where we assess the same group or related groups across different conditions or time points. The ranking of ordinal data aligns perfectly with the assumptions of Friedman's test, which seeks to compare the ranks rather than the actual values. While skewed data can sometimes be analyzed using different statistical methods, they do not match the specific requirements of Friedman's ANOVA as effectively as ordinal data do. Similarly, normal data generally fits the assumptions of parametric tests, like standard ANOVA, and nominal data, which lacks an inherent order, wouldn't provide meaningful results in the context of Friedman’s ranking methodology. Thus, the application of Friedman's ANOVA is most appropriate when dealing with ordinal data.