# Mauchly test

## Mauchly test :

The Mauchly test is a statistical test used to determine if the assumption of sphericity has been violated in a repeated measures analysis of variance (ANOVA). This assumption states that the variances of the differences between all pairs of levels of the within-subjects factor are equal. Violation of this assumption can result in biased and inaccurate estimates of the effects of the within-subjects factor, as well as incorrect p-values and Type I error rates.
One example of the Mauchly test is in a study examining the effects of different exercise interventions on weight loss. The study includes three different exercise interventions (aerobic, resistance, and combination) and measures weight loss at three different time points (baseline, 6 weeks, and 12 weeks). In this study, the within-subjects factor is the time point, and the between-subjects factor is the exercise intervention.
To conduct the Mauchly test, the researcher first calculates the variances of the differences between all pairs of levels of the within-subjects factor (in this case, the differences between baseline, 6 weeks, and 12 weeks). If the variances of these differences are not equal, the assumption of sphericity is violated and the Mauchly test is significant.
In this study, if the variances of the differences between baseline, 6 weeks, and 12 weeks are not equal, it indicates that the weight loss data is not evenly distributed across the three time points. This could be due to factors such as individual differences in weight loss rates or the effectiveness of the exercise interventions.
In this case, the researcher would need to use a correction method, such as the Greenhouse-Geisser or Huynh-Feldt, to account for the violation of the assumption of sphericity and obtain accurate estimates of the effects of the time point and exercise intervention on weight loss.
Another example of the Mauchly test is in a study examining the effects of different teaching methods on student achievement. The study includes three different teaching methods (lecture, discussion, and cooperative learning) and measures student achievement at three different grades (3rd, 4th, and 5th). In this study, the within-subjects factor is the grade, and the between-subjects factor is the teaching method.
To conduct the Mauchly test, the researcher first calculates the variances of the differences between all pairs of levels of the within-subjects factor (in this case, the differences between 3rd, 4th, and 5th grades). If the variances of these differences are not equal, the assumption of sphericity is violated and the Mauchly test is significant.
In this study, if the variances of the differences between 3rd, 4th, and 5th grades are not equal, it indicates that the student achievement data is not evenly distributed across the three grades. This could be due to factors such as individual differences in learning abilities or the effectiveness of the teaching methods.
In this case, the researcher would need to use a correction method, such as the Greenhouse-Geisser or Huynh-Feldt, to account for the violation of the assumption of sphericity and obtain accurate estimates of the effects of the grade and teaching method on student achievement.