What does it mean if Greenhouse-Geisser is significant?

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.

What is sphericity and how do we interpret it?

Sphericity. This means that the population variances of all possible difference scores (com_1 – com_2, com_1 – com_3 and so on) are equal. Sphericity is tested with Mauchly’s test which is always included in SPSS’ repeated measures ANOVA output so we’ll get to that later.

When might you use the Greenhouse-Geisser correction?

Greenhouse-Geisser vs. 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.

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

→ 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.

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 significance of sphericity?

Sphericity is a measure of the degree to which a particle approximates the shape of a sphere, and is independent of its size. Roundness is the measure of the sharpness of a particle’s edges and corners.

What is a sphericity in geography?

sphericity (sphe-ric’-i-ty). True sphericity, as originally defined by Wadell (1932), is the ratio of the surface area of a sphere of the same volume as the particle to the actual surface area of the particle.

What does the assumption of sphericity have to do with spheres?

Sphericity is the condition where the variances of the differences between all combinations of related groups (levels) are equal. Sphericity can be likened to homogeneity of variances in a between-subjects ANOVA.

What is the appropriate null hypothesis for Mauchly’s test of sphericity?

Only reported for variables or effects with >2 levels because sphericity necessarily holds for effects with only 2 levels. The null hypothesis is that the variances of the group differences are equal.

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

What is sphericity used to find?

Sphericity gives you one way of approximating how close objects are to sphere. You can, for example, calculate the sphericity as an approximation the Earth’s shape which is, in fact, not a perfect sphere.

What is the Greenhouse-Geisser correction?

What is the difference between Greenhouse Geisser and Huynh Feldt?

Of the two sphericity correction methods, Huynh-Feldt correction is considered the least conservative (overestimate epsilon), while Greenhouse–Geisser is considered more conservative (underestimate epsilon when epsilon is close to 1). The general recommendation is to use the Greenhouse-Geisser correction, particularly when epsilon < 0.75.

What is Epsilon in Greenhouse-Geisser?

Sphericity (cont…) The Greenhouse-Geisser procedure estimates epsilon (referred to as ) in order to correct the degrees of freedom of the F -distribution as has been mentioned previously, and shown below: Using our prior example, and if sphericity had been violated, we would have:

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.