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. 2008 Feb 16;336(7640):361–365. doi: 10.1136/bmj.39476.623611.25

Table 2.

 Sources of variation in measured outcomes in randomised controlled trials

Label Source Description
T Between treatments Variation caused by average effect of treatment
B Between patients Variation caused by differences between patients unrelated to treatment
W Within patients Variation caused by measurement variability
R Between patients in treatment effect Variation caused by differences between patients in effect of treatment