Sphericity

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” rows,] Not violating this assumption means that the F-statistic that you have calculated is valid and can be used to determine statistical significance,

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In SPSS, the “Sphericity Assumed” rows are where sphericity has not been violated, and therefore, represents the normal calculations we would make to calculate a significance value for a repeated measures ANOVA, Notice how the sum of squares and F-statistic are identical regardless of whether or which correction is applied shown below in blue, This further highlights that the corrections

Data Assumption: Sphericity

SPSS provides an F-value for when sphericity is assumed, as well as options for corrections applied to produce a valid F-value, Among them are the Greenhouse-Geisser corrected F-value and the Huynh-Feldt F-value, The heuristic is that when Mauchly’s sphericity Mauchly’s W is greater than 0,75, then use Huynh-Feldt, and when less than 0,75 or unknown, use Greenhouse …

What does sphericity assumed mean?

Mauchly’s Test of Sphericity indicated that the assumption of sphericity had not been violated, χ 2 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” rows,]

SPHERICITY IN REPEATED MEASURES ANALYSIS OF VARIANCE

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Sphericity requires that the variances for each set of difference scores be equal, Put simplistically, we assume that the relationship between pairs of pairs of groups is similar i,e,, the level of dependence between pairs of groups is roughly equal, We have been taught that it is critical to have homogeneity of variance between conditions when analyzing data from different participants

SPSS Tip 15,1 My Mauchly’s test looks weird

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Discovering Statistics Using IBM SPSS Statistics Although the result seems plausible, we have learnt that departures from sphericity make the F-test inaccurate, and Output 15,2 shows that these data are not spherical, As well as showing the F-statistic and associated degrees of freedom when sphericity is assumed, Output 15,4 shows the results adjusted using the three estimates of sphericity in

Use and Interpret Greenhouse-Geisser in SPSS

When the assumption of sphericity is violated with repeated-measures ANOVA, then the Greenhouse-Geisser correction is used, The steps for conducting a Greenhouse-Geisser correction in SPSS , 1, The data is entered in a within-subjects fashion, 2, Click Analyze, 3, Drag the cursor over the General Linear Model drop-down menu, 4, Click Repeated Measures, 5, Type the number of observations of the

Mauchly’s Test of Sphericity with Repeated Measures ANOVA

This video demonstrates how to calculate and interpret Mauchly’s test of sphericity with Repeated Measures ANOVA in SPSS, Methods of how to proceed if the as

SPSS Repeated Measures ANOVA

What Is Repeated Measures ANOVA?

Repeated measures within-subjects ANOVA

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p > 0,05, Sphericity can be assumed, Use the p-value from the Greenhouse-Geisser correction row in the ‘Tests of Within -Subjects Effects’ ANOVA table , Data: Participants used Clora margarine for 8 weeks, Their cholesterol in mmol/L was measured before the special diet, after 4 weeks and after 8 weeks, Open the SPSS file ‘Cholesterol,sav’ and follow the instructions to see if the

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From Chapter 8 of my *free* textbook: How2statsbook,Download the chapters here: www,how2statsbook,comMore chapters to come, Subscribe to be notified,

A Bluffer’s Guide to Sphericity

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SPSS produces three corrections based upon the estimates of sphericity advocated by Greenhouse and Geisser 1958 and Huynh and Feldt 1976, Both of these estimates give rise to a correction factor that is applied to the degrees of freedom used to asses the observed value of F , How each estimate is calculated is beyond the scope of this article, for our purposes all we need know is that each

SPSS Repeated Measures ANOVA

SPSS RM Anova – 2 Within-Subjects Factors