How is Greenhouse-Geisser correction calculated?

How is Greenhouse-Geisser correction calculated?

To correct for this inflation, multiply the Greenhouse–Geisser estimate of epsilon to the degrees of freedom used to calculate the F critical value. An alternative correction that is believed to be less conservative is the Huynh–Feldt correction (1976).

What is Greenhouse-Geisser correction factor?

The Greenhouse-Geisser is used to assess the change in a continuous outcome with three or more observations across time or within-subjects. In most cases, the assumption of sphericity is violated for this type of within-subjects analysis and the Greenhouse-Geisser correction is robust to the violation.

Should I use greenhouse-Geisser or Huynh Feldt?

Generally, the recommendation is to use the Greenhouse-Geisser correction, especially if estimated epsilon (ε) is less than 0.75. However, some statisticians recommend using the Huynd-Feldt correction if estimated epsilon (ε) is greater than 0.75.

When should you apply a sphericity correction to a repeated measures analysis?

Sphericity can be evaluated when there are three or more levels of a repeated measure factor and, with each additional repeated measures factor, the risk for violating sphericity increases. If sphericity is violated, a decision must be made as to whether a univariate or multivariate analysis is selected.

What does it mean if Mauchly’s test of sphericity is significant?

Assessing the Severity of Departures from Sphericity → If Mauchly’s test statistic is significant (i.e. has a probability value less than . 05) we conclude that there are significant differences between the variance of differences: the condition of sphericity has not been met.

What does Mauchly’s test of sphericity tell you?

Mauchly’s Test of Sphericity indicated that the assumption of sphericity had not been violated, χ2(2) = 3.343, p = . If your data does not violate the assumption of sphericity, you do not need to modify your degrees of freedom. [If you are using SPSS, your results will be presented in the “sphericity assumed” row(s).]

How do I report Mauchly’s sphericity?

In other words the assumption of sphericity has been violated. We could report Mauchly’s test for these data as: → Mauchly’s test indicated that the assumption of sphericity had been violated, χ2(5) = 11.41, p = . 047.

What is the Greenhouse Geisser correction used for?

The Greenhouse–Geisser correction is a statistical method of adjusting for lack of sphericity in a repeated measures ANOVA. The correction functions as both an estimate of epsilon (sphericity) and a correction for lack of sphericity. The correction was proposed by Samuel Greenhouse and Seymour Geisser in 1959.

How do I use the Greenhouse-Geisser correction for repeated measures ANOVA?

When the assumption of sphericity is violated with repeated-measures ANOVA, then the Greenhouse-Geisser correction is used. 1. The data is entered in a within-subjects fashion. 2. Click A nalyze. 3. Drag the cursor over the G eneral Linear Model drop-down menu.

How do you interpret the p-value of a Greenhouse-Geisser test?

1. In the Tests of Within-Subjects Effects table, look under the Sig. column for the Greenhouse-Geisser row value. This is the p -value that is interpreted. In the Partial Eta Squared column, there is a measure of effect size for the analysis.

What is the difference between Greenhouse Geisser and huynd Feldt?

Greenhouse-Geisser vs. Huynd-Feldt Correction The Greenhouse-Geisser correction tends to underestimate epsilon (ε) when epsilon (ε) is close to 1 (i.e., it is a conservative correction), whilst the Huynd-Feldt correction tends to overestimate epsilon (ε) (i.e., it is a more liberal correction).