Two studies in the New England Journal of Medicine did not confirm this rule of thumb for Evidence Based Medicine.
A comparison between randomized controlled trials with observational studies in 19 therapeutic areas and meta analyses of RCT’s with meta-analyses of cohort and case control studies in 5 therapeutic areas did not find a difference in treatment effect.
What is the difference between RCT and an Observational study?
RCTs involve the random allocation of different interventions (or treatments) to subjects. This ensures that confounding factors are evenly distributed between treatment groups.
The goal of an observational study is to draw inferences about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator. This is in contrast with controlled experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group before the start of the treatment.
Explanations for the lack of differences in outcome between RCTs and observational studies emerged in the BMJ: Which clinical studies provide the best evidence?:
- Observational studies have improved
- Selection of publications limited to well known journals
- One observational study did not involve treatment but risk factors in the general population
- Some of the results of the meta-analyses and RCT’s were falsified in more recent trials, e.g.screening for breast cancer was not found to be of benefit and hormone replacement therapy in menopausal women did not prevent coronary risk nor fracture risk
Objections to the use of observational studies:
- Observational studies are mostly performed in institutions with better quality of care for that specific group
- Selection of patients with a larger capacity to benefit
- Publication bias against negative results
Now what is the best evidence?
Randomized Controlled Trials when well conducted are the golden standard. However small inadequate RCT’s are not better than a well conducted conflicting observational study.
Well done observational studies are preferred above lousy RCT’s.
But what is a well-done observational study?
A good observational study adheres the STROBE statement.
What is STROBE?
STROBE stands for an international, collaborative initiative of epidemiologists, methodologists, statisticians, researchers and journal editors involved in the conduct and dissemination of observational studies, with the common aim of
STrengthening the Reporting of OBservational studies in Epidemiology.
Observational research comprises several study designs and many topic areas. We aimed to establish a checklist of items that should be included in articles reporting such research – the STROBE Statement. We considered it reasonable to initially restrict the recommendations to the three main analytical designs that are used in observational research: cohort, case-control, and cross-sectional studies. We want to provide guidance on how to report observational research well. Our recommendations are not prescriptions for designing or conducting studies. Also, the checklist is not an instrument to evaluate the quality of observational research.
With thses guidelines and the website of Strobe, observational studies can be of importance to clinicians and patients. We shouldn’t forget that observational studies laid the foundations for important clinical achievements such as the discovery of AIDs, the relationship between smoking and lung cancer, and the relationship between flying and thrombosis.
The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: Guidelines for Reporting Observational Studies
von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, et al.
PLoS Medicine Vol. 4, No. 10, e296 doi:10.1371/journal.pmed.0040296