Did intervention studies use predominantly non-experimental research designs?
Of the nine intervention studies in 1987–1988, five were controlled experimental designs (two randomised controlled trials, three non-randomised controlled trials) and four were non-experimental designs (two single-group designs; two described only process variables or components of the intervention delivered rather than outcomes). Of the 36 intervention studies in 1997–1998, nine (25%) were controlled experimental designs (five randomised controlled trials, four non-randomised controlled trials) and 27 were non-experimental designs (four cohort or longitudinal studies, one case–control study, 22 single-group designs). Of the 31 intervention studies in 2001–2003, three were controlled experimental designs (randomised controlled trials) and 28 were non-experimental designs (15 longitudinal studies, two case–control studies, 11 single-group designs).
