Control group definition3/29/2023 ![]() ( Papageorgiou et al 2017) investigated how the use of historical controls rather than contemporaneous controls affected the effect estimates derived from clinical trials of orthodontic interventions: they found that use of historical controls produced smaller estimates of effect (across 13 meta-analyses the standardised mean difference was reduced by 0.31 (95% CI = 0.10 to 0.53). However, Other factors could have changed between the two-time points, such as the degree of ill health of the infants, improvements in medical care and new treatments. The researchers, therefore, used a pragmatic evaluation by selecting a historical comparison group (they obtained data on outcomes for infants before the introduction of the intervention). The intervention had already been implemented. The intervention aimed to improve the coping capacity of parents, reduce the length of hospital stay and readmission rates. ExampleĪn intervention study using historical controls assessed the effect of a psychosocial intervention programme for parents of premature infants ( Gonya et al. Historical and contemporaneous cohort studies can be used to examine rare exposures and multiple effects of a single exposure over time. However, this risks introducing non-contemporaneous control bias as, over time, factors affecting controls and their experiences whic may have changed, obscure or exaggerate relationships For practical reasons, this can be a useful approach since it avoids the need to collect new information for the control group. Changes in disease or diagnostic definitions, exposures over time, and treatments, could all contribute to non-contemporaneous bias.Ĭase-control studies sometimes use historical controls. If, in a case-control study, cases are selected during one period and controls are selected during another period, then the relationships observed between exposures and outcomes of interest may be affected. ![]()
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |