The Intraclass Corrrelation Coefficient as an …



(2 for Random Effects, aka the Intraclass Correlation Coefficient(

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Lori Foster Thompson provided me with data from 40 teams, each consisting of 4 persons. Twenty of the teams were in an experimental group referred to as “face to face” (FTF) and the other twenty were in the “computer-mediated” (CM) group. The dependent variable was the score on a five item scale designed to measure satisfaction with the team process. Lori compared the two groups using individual persons as the experimental unit -- that is, she had 4 x 40 = 160 cases, 80 in each of two groups. I replicated this analysis using a pooled variances t (equivalent to a one-way ANOVA). This analysis showed that satisfaction in the FTF group (M = 4.25, s = 0.70) was significantly greater than in the CM group (M = 3.33, SD = 0.83), t(158) = 7.54, p < .001. If this comparison was made with ANOVA rather than t, the F would be the square of the t -- F(1, 158) = 58.86, p  F

Model 39 71.1840000 1.8252308 3.96 F

TM_NO2 39 71.18400000 1.82523077 3.96 F

TM_NO2 39 71.184000 1.825231 3.96 F

Model 39 71.1840000 1.8252308 3.96 F

CONDTN 1 33.48900000 33.48900000 72.59 F

CONDTN 1 33.489000 33.489000 33.76 F

TM_NO2(CONDTN) 38 37.695000 0.991974 2.15 0.0009

Error: MS(Error) 120 55.360000 0.461333

Note that the SS for Teams from the previous analysis, 71.184, has been partitioned into a SS for Condtn, 33.489, and a SS for Teams within conditions, 37.695. The Total SS (126.544) is comprised of the SS for Condtn, 33.489, plus the SS for Teams within conditions, 37.695, plus the SS for Subjects within teams within conditions, 55.36. Do note that the analysis above uses the variance for teams within conditions as the error variance for testing the effect of Condtn.

The (2 for the entire effect of teams is 71.184/126.544 = .563. That part due to the experimental manipulation is 33.489/126.544 = .265.

References

Howell, D. C. (2007). Statistical methods for psychology (6th ed.). Belmont, CA: Thompson Wadsworth.

Howell, D. C. (2010). Statistical methods for psychology (7th ed.). Belmont, CA: Cengage Wadsworth.

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Copyright 2010, Karl L. Wuensch - All rights reserved.

( Copyright 2010, Karl L. Wuensch - All rights reserved.

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