Solved – Repeated measures or two-way ANOVA, and power analysis

anovarepeated measuresstatistical-power

A sample of patients will undergo two treatments. Every patient will receive both treatments.One treatment will on the left side and the other different treatment on the right side. Repeated measurements will be done for each side at several time intervals.

My questions are:

Which analysis is appropriate for that case. Two-way ANOVA with treatment and time being the factors, or simply a repeated measures ANOVA because of the two sides dependency.
If it's the latter test, for sample size calculation, should I use in Gpower the ANOVA: repeated measures,within-between interaction option
If it's the two-way ANOVA, how to calculate the sample size for that? Any software?

Best Answer

For your third question, GPOWER (current version) permits one and two-tailed tests as an option.

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Solved – One-way repeated measures ANOVA with G*Power

I think I found it here:

Link to book chapter, additional material

Applied to my problem I guess it will be like this:

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F tests - ANOVA: Repeated measures, within factors
Analysis:   Criterion: Compute required α 
Input:  Effect size f   =   0.25
    Power (1-β err prob)    =   0.80
    Total sample size   =   28
    Number of groups    =   1
    Number of measurements  =   3
    Corr among rep measures =   0.3
    Nonsphericity correction ε  =   1
Output: Noncentrality parameter λ   =   7.5000000
    Critical F  =   2.2129741
    Numerator df    =   2.0000000
    Denominator df  =   54.0000000
    α err prob  =   0.1191999

Solved – Unequal sample sizes for two-way repeated measures

Look into linear mixed effects modelling, it can handle missing repeats which the standard anova linear modelling approach cannot.

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Related Solutions

Solved – One-way repeated measures ANOVA with G*Power

Solved – Unequal sample sizes for two-way repeated measures

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