08_RB_2

# 08_RB_2 - Intraclass Correlation It is a effect size for...

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Intraclass Correlation • It is a effect size for the block effect. | 1 ˆ (1 ) BL IYBL A BL F p F ρ= −+ | 17.4 1 ˆ 0.89 (2 1) 17.4 = (e.g.) (This is an extremely high intraclass correlation) • It indicates the amount of variance explained by blocking. • It is also an indication of the amount of improvement of the analysis by design. More improvement with a higher intraclass correlation. (computational formula) • A typical use of the intraclass correlation is the adjustment of effect size from completely randomized design. * .40 .478 11 . 3 0 f f == = −ρ (e.g.) • Assume p = 3, and that you can expect a large effect size ( f = .40) by a completely randomized design (i.e., without blocking – Oneway ANOVA). • Assume you can expect an intraclass correlation of .30 by blocking in randomize block design. • Then, the equivalent effect size in the randomized block design is:

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• This adjusted effect size can be used in the estimation of required sample size. (e.g., p = 4, α = 0.05, 1 – β = 0.8) v 1 = 3, v 2 RB = 3( n –1), f = .478 Then, n = 13 (total of = 13 × 4 = 52). On the other hand, with completely randomized design, v 1 = 3, v 2 CR = 4( n f = .400 Then, n =18 (total of 18 × 4 = 72). RB- p design as repeated measures: • As mentioned before, one method of blocking is to obtain a set of repeated measures. • In other words, measures are obtained p times from each of n people.
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## This note was uploaded on 11/27/2011 for the course EDF 5402 taught by Professor Thomasbaldwin during the Fall '09 term at FSU.

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08_RB_2 - Intraclass Correlation It is a effect size for...

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