Skip to main content
. 2008 Aug;98(8):1418–1424. doi: 10.2105/AJPH.2007.127027

TABLE 1—

Formulas for the Variance of the Difference Between 2 Study Conditions: Pretest–Posttest GRT and IRGT Trial Study Designs

Repeated Measures Analysis of Variance Analysis of Covariance With Baseline as Covariate
Study design
    GRT: 2 conditions Inline graphic Inline graphic
    IRGT trial: 2 group treatment conditions Inline graphic Inline graphic
    IRGT trial: 1 group treatment condition and 1 individual treatment condition Inline graphic Inline graphic
Detectable differencea (all study designs) Inline graphic

Note. GRT = group-randomized trial; IRGT = individually randomized group treatment; σ̂2m = member component of variance; r^yy(m) = over-time correlation at the member level; m = average number of members per group (nested within study condition); σ̂2m = group component of variance; N1 = number of participants in individual treatment condition; N2 = number of participants in group treatment condition; Δ̂ = detectable difference (between study conditions); σ̂2Δ = variance of the difference between study conditions.

aSmallest difference between study conditions that would be considered significant.