title: Evaluating Group-Based Interventions When Control Participants Are Ungrouped.
abstract: Individually randomized treatments are often administered within a group setting. As a consequence, outcomes for treated individuals may be correlated due to provider effects, common experiences within the group, and/or informal processes of socialization. In contrast, it is often reasonable to regard outcomes for control participants as independent, given that these individuals are not placed into groups. Although this kind of design is common in intervention research, the statistical models applied to evaluate the treatment effects are usually inconsistent with the resulting data structure, potentially leading to biased inferences. This article presents an alternative model that explicitly accounts for the fact that only treated participants are grouped. In addition to providing a useful test of the overall treatment effect, this approach also permits one to formally determine the extent to which treatment effects vary over treatment groups and whether there is evidence that individuals within treatment groups become similar to one another. This strategy is demonstrated with data from the Reconnecting Youth program for high school students at risk of school failure and behavioral disorders.
authors.affiliation: University of North Carolina at Chapel Hill.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Bauer
authors.forename: Sonya K
authors.initials: SK
authors.lastname: Sterba
authors.forename: Denise Dion
authors.initials: DD
authors.lastname: Hallfors
references.citation: Clin Trials. 2005;2(2):152-62
references.pmid: 16279137
references.citation: Psychol Methods. 2003 Dec;8(4):535-44
references.pmid: 14664688
references.citation: Psychol Methods. 2003 Dec;8(4):497-517
references.pmid: 14664685
references.citation: J Consult Clin Psychol. 2005 Oct;73(5):924-35
references.pmid: 16287392
references.citation: J Consult Clin Psychol. 1991 Feb;59(1):20-6
references.pmid: 2002139
references.citation: Am J Public Health. 2006 Dec;96(12):2254-9
references.pmid: 16809591
references.citation: Psychol Methods. 2000 Dec;5(4):425-33
references.pmid: 11194206
references.citation: J Pers Soc Psychol. 2002 Jul;83(1):126-37
references.pmid: 12088122
references.citation: Biometrics. 1997 Sep;53(3):983-97
references.pmid: 9333350
references.citation: Health Educ Res. 2007 Feb;22(1):95-107
references.pmid: 16807378
references.citation: Psychol Methods. 2003 Dec;8(4):524-34
references.pmid: 14664687
references.citation: Am J Public Health. 2004 Mar;94(3):423-32
references.pmid: 14998806
references.citation: Clin Trials. 2005;2(2):163-73
references.pmid: 16279138
references.citation: J Consult Clin Psychol. 2004 Dec;72(6):1038-49
references.pmid: 15612850
references.citation: J Consult Clin Psychol. 2004 Apr;72(2):252-68
references.pmid: 15065959
references.citation: Multivariate Behav Res. 2001 Apr 1;36(2):155-83
references.pmid: 26822107
references.citation: Am J Health Promot. 1994 Jan-Feb;8(3):202-15
references.pmid: 10172017
references.citation: Addict Behav. 2004 May;29(3):595-606
references.pmid: 15050677
references.citation: BMC Med Res Methodol. 2004 Aug 13;4:21
references.pmid: 15310402
references.citation: J Consult Clin Psychol. 2005 Oct;73(5):914-23
references.pmid: 16287391
references.citation: Eval Rev. 2003 Feb;27(1):79-103
references.pmid: 12568061
references.citation: J Abnorm Child Psychol. 2005 Jun;33(3):363-74
references.pmid: 15957563
references.citation: Psychol Methods. 2003 Dec;8(4):518-23
references.pmid: 14664686
references.citation: Psychol Methods. 2000 Jun;5(2):199-213
references.pmid: 10937329
references.citation: Multivariate Behav Res. 1995 Jan 1;30(1):1-21
references.pmid: 26828342
references.citation: J Consult Clin Psychol. 2005 Dec;73(6):1036-44
references.pmid: 16392977
references.citation: Stat Med. 2002 May 30;21(10):1351-64
references.pmid: 12185889