Basic study design influences the results of orthodontic clinical investigations

Abstract

Objectives Meta-analysis is the gold standard for synthesizing evidence on the effectiveness of health care interventions. However, its validity is dependent on the quality of included studies. Here, we investigated whether basic study design (i.e., randomization and timing of data collection) in orthodontic research influences the results of clinical trials. Study design and setting This meta-epidemiologic study used unrestricted electronic and manual searching for meta-analyses in orthodontics. Differences in standardized mean differences (ΔSMD) between interventions and their 95% confidence intervals (CIs) were calculated according to study design through random-effects meta-regression. Effects were then pooled with random-effects meta-analyses. Results No difference was found between randomized and nonrandomized trials (25 meta-analyses; ΔSMD = 0.07; 95% CI = -0.21, 0.34; P = 0.630). However, retrospective nonrandomized trials reported inflated treatment effects compared with prospective (40 meta-analyses; ΔSMD = -0.30; 95% CI = -0.53, -0.06; P = 0.018). No difference was found between randomized trials with adequate and those with unclear/inadequate generation (25 meta-analyses; ΔSMD = 0.01; 95% CI = -0.25, 0.26; P = 0.957). Finally, subgroup analyses indicated that the results of randomized and nonrandomized trials differed significantly according to scope of the trial (effectiveness or adverse effects; P = 0.005). Conclusion Caution is warranted when interpreting systematic reviews investigating clinical orthodontic interventions when nonrandomized and especially retrospective nonrandomized studies are included in the meta-analysis.