2-5 People should not know which treatment they get

People in a treatment group may experience improvements (for example, less pain) because they believe they are receiving a better treatment, even if the treatment is not actually better (this is called a placebo effect), or because they behave differently (due to knowing which treatment they received, compared to how they otherwise would have behaved). If individuals know that they are receiving (they are not “blinded” to) a treatment that they believe is better, some or all of the apparent effects of the treatment may be due either to a placebo effect or because the recipients behaved differently.

Be cautious about relying on the results of treatment comparisons if the participants knew which treatment they were receiving, this may have affected their expectations or behaviour. The results of such comparisons could be misleading.

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Know Your Chances

This book has been shown in two randomized trials to improve peoples' understanding of risk in the context of health care choices.

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Defining Bias

This blog explains what is meant by ‘bias’ in research, focusing particularly on attrition bias and detection bias.


CEBM – Study Designs

A short article explaining the relative strengths and weaknesses of different types of study design for assessing treatment effects.


Pre-eclampsia in pregnant women

Another outstanding example of good research concerns pregnant women. Worldwide, about 600,000 women die each year of pregnancy-related complications. Most […]


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