Transcription of Experimental design and sample size determination
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Experimental design and sample size determination
1 Experimental 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 design3 Basic question/goal in (aka blocking) experiments43 ExampleQuestion: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).64 Replication7 Why replicate? Reduce the effect of uncontrolled variation( , increase precision). Quantify related point:An estimate is of no value without some statement of the uncertainty in the subjects ( units ) should be assigned totreatment groups at random does not mean needs to explicitly randomize using A computer, or Coins, dice or randomize?
Note • This is a shortened version of a lecture which is part of a web- ... •Good design and good analysis can lead to reduced sample sizes. ... 140.615-616, Johns Hopkins Bloomberg Sch. Pub. Health) –Intoductory statistics course, intended for experimental scientists.
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