Study Design and Sample Size HRB revised 130910 …
Study DesignandSample SizeProfessor Leslie Daly9thSept, 20102If only I had a centfor every time I was askedHow many patientsdo I need for my Study ?3Advice to a StatisticalConsultant:There is no such thing as a Sample size size is but one aspect of Study Design . Whenyou are asked to help determine the Sample sizea lot of questions must be asked and answeredbefore you get to that may often end upneverdiscussing Sample size because there areother matters that override it in (2001)4It seems an easy question, likeHow much moneyshould I take on my holidays?5Why is the Sample SizeImportant? Ethical reasons: Proper use of scarce resources You don t want a Study that won t show anything because it s too small You don t want a Study that is too big when a smaller one would have done Funding agencies require it6How many?
34 Usual Formulae are for Equal Sample Sizes Designing a study with equal sample sizes in two comparison groups is most efficient When might you have unequal n? –Cross-sectional …
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