Experimental design and sample size determination

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1Experimental designand sample size determinationKarl W BromanDepartment of BiostatisticsJohns Hopkins ~kbromanNote This is a shortened version of a lecture which is part of a web-based course on Enhancing Humane Science/ImprovingAnimal Research (organized by Alan Goldberg, Johns HopkinsCenter for Alternatives to Animal Testing) Few details mostly design3Basic question/goal in (aka blocking) experiments43ExampleQuestion:Does salted drinking water affect blood pressure (BP) in mice? a mouse with water containing 1% 14 experiments are comparative. Compare BP in mice fed salt water to BP in micefed plain water. Compare BP in strain A mice fed salt water to BPin strain B mice fed salt , the Experimental group is compared toconcurrent controls (rather than to historical controls).

Sample size determination 24. 13 Fundamental formula $ per sample $ available n= 25 Listen to the IACUC Too few animals → a total waste Too many animals → a partial waste 26. 14 Significance test • Compare the BP of 6 mice fed salt water to 6 mice fed plain water. • Δ = true difference in average BP (the treatment effect).

  Tests, Samples, Size, Determination, Sample size determination