Essential Clinical Epidemiology Randomized Controlled Trial Anna Keski-Rahkonen Pyry Sipilä Clinicum, Department of Public Health
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“God doesn't play dice with the universe.” Albert Einstein Want to know more about God playing dice with the universe?
RCT, Basic Study Design Treatment Group Control Group Outcome Outcome YES NO YES NO Slide adapted from Lorraine Alexander & Karen Yeatts
Randomization • Sound randomization will on average distribute all known and unknown confounding factors equally to different arms (groups) of the study. • This can be affected by chance, of course.
The Cult of the RCT
RCT – common problems • Something goes wrong with the randomization • Intention to treat analysis not conducted
Allocation concealment DATA CENTER Making sure that randomization will occur -> Removing selection bias
Who is Blind? Participant Researcher Data Analyst
Intention to Treat, Basic Principle:
ITT • Anything nonrandom (completion of study, problems in allocaion concelment etc. etc.) will make the RCT an observational study. • An observational study in the disguise of RCT has all the pitfalls of any other observational study - and potentially worse. • RCTs have usually not been designed to adequately control for confounding.
RCTs, Advantages & Disadvantages • Advantages: • unbiased distribution of confounders; • blinding more likely; • randomisation facilitates statistical analysis. • Disadvantages: • expensive: time and money; • volunteer bias; • ethically problematic at times. Slide: Oxford University, Centre for Evidence-Based Medicine
“All RCTs do is show that what you’re dealing with is not snake oil.” Ben Williams
PI CO Que stio ns • P = Pa tie nt / Pro b le m • I = I nte rve ntio n • C = Co mpa riso n/ Co ntro l • O = Outc o me
What is a Large Effect? Effect Sizes: Cohen’s d • Cohen classified effect sizes as • small ( d = 0.2), • medium ( d = 0.5), and • large ( d ≥ 0.8). 5 • “A medium effect of .5 is visible to the naked eye of a careful observer. A small effect of .2 is noticeably smaller than medium but not so small as to be trivial. A large effect of .8 is the same distance above the medium as small is below it.” https://youtu.be/0sSHqWzqq -I
Visualize with your pair using bit.do/effectsize How the distributions in the intervention and control group differ • small ( d = 0.2), • medium ( d = 0.5), and • large ( d ≥ 0.8). • “A medium effect of .5 is visible to the naked eye of a careful observer. A small effect of .2 is noticeably smaller than medium but not so small as to be trivial. A large effect of .8 is the same distance above the medium as small is below it.”
Power Calculations https://youtu.be/P2Z6u8hwl2U
Practical Problem Observational studies: Low levels of serum Vitamin D3 -> more cancer & cardiovascular disease cancer↓ ? → cardiovascular disease↓ ?
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