TY - JOUR
T1 - Analysis of data from group-randomized trials with repeat observations on the same groups
AU - Murray, David M.
AU - Hannan, Peter J
AU - Wolfinger, Russell D.
AU - Baker, William L.
AU - Dwyer, James H.
PY - 1998/7/30
Y1 - 1998/7/30
N2 - This study used Monte Carlo simulations to evaluate the performance of alternative models for the analysis of group-randomized trials having more than two time intervals for data collection. The major distinction among the models tested was the sampling variance of the intervention effect. In the mixed-model ANOVA, the sampling variance of the intervention effect is based on the variance among group x time-interval means. In the random coefficients model, the sampling variance of the intervention effect is based on the variance among the group-specific slopes. These models are equivalent when the design includes only two time intervals, but not when there are more than two time intervals. The results indicate that the mixed-model ANOVA yields unbiased estimates of sampling variation and nominal type I error rates when the group-specific time trends are homogenous. However, when the group-specific time trends are heterogeneous, the mixed-model ANOVA yields downwardly biased estimates of sampling variance and inflated type I error rates. In contrast, the random coefficients model yields unbiased estimates of sampling variance and the nominal type I error rate regardless of the pattern among the groups. We discuss implications for the analysis of group-randomized trials with more than two time intervals.
AB - This study used Monte Carlo simulations to evaluate the performance of alternative models for the analysis of group-randomized trials having more than two time intervals for data collection. The major distinction among the models tested was the sampling variance of the intervention effect. In the mixed-model ANOVA, the sampling variance of the intervention effect is based on the variance among group x time-interval means. In the random coefficients model, the sampling variance of the intervention effect is based on the variance among the group-specific slopes. These models are equivalent when the design includes only two time intervals, but not when there are more than two time intervals. The results indicate that the mixed-model ANOVA yields unbiased estimates of sampling variation and nominal type I error rates when the group-specific time trends are homogenous. However, when the group-specific time trends are heterogeneous, the mixed-model ANOVA yields downwardly biased estimates of sampling variance and inflated type I error rates. In contrast, the random coefficients model yields unbiased estimates of sampling variance and the nominal type I error rate regardless of the pattern among the groups. We discuss implications for the analysis of group-randomized trials with more than two time intervals.
UR - http://www.scopus.com/inward/record.url?scp=0032581453&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032581453&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1097-0258(19980730)17:14<1581::AID-SIM864>3.0.CO;2-N
DO - 10.1002/(SICI)1097-0258(19980730)17:14<1581::AID-SIM864>3.0.CO;2-N
M3 - Article
C2 - 9699231
AN - SCOPUS:0032581453
SN - 0277-6715
VL - 17
SP - 1581
EP - 1600
JO - Statistics in Medicine
JF - Statistics in Medicine
IS - 14
ER -