Description: The Friedman test is a non-parametric statistical test used to detect differences in treatments across multiple test attempts. It is applied in situations where there are three or more related groups and seeks to evaluate whether there are significant differences in their medians. Unlike ANOVA, which assumes normality in the data, the Friedman test does not require the data to follow a normal distribution, making it especially useful in studies where this assumption is not met. The test is based on the ranks of the observations and is commonly used in repeated measures experiments, where the same subjects are evaluated under different conditions. Its result is expressed through a statistic that is compared to a chi-square distribution to determine significance. The Friedman test is valued for its ability to handle ordinal data and its robustness against assumption violations, making it a valuable tool in scientific research and data analysis across various disciplines.
History: The Friedman test was developed by American statistician Milton Friedman in 1937. Its creation is set against a backdrop where the need for statistical methods that did not rely on the normality of data was becoming increasingly evident, especially in the fields of psychology and social sciences. Since its introduction, the test has evolved and been integrated into various research areas, becoming a standard tool for non-parametric data analysis.
Uses: The Friedman test is primarily used in studies where there is a need to compare three or more related groups. It is common in research in psychology, medicine, and social sciences, where researchers often work with ordinal or non-normally distributed data. It is also applied in experimental design studies, where different treatments or conditions are evaluated on the same subjects.
Examples: A practical example of the Friedman test could be a study evaluating the effectiveness of three different treatments for anxiety in a group of patients. The same patients are assessed at different times after receiving each treatment, and the Friedman test is used to determine if there are significant differences in anxiety levels between the treatments. Another example could be an experiment measuring student performance on three different exams throughout a semester.
