Determining the Source of Variability

The statistical analyses that you have in mind for testing the main hypotheses may require you to explore the cause of variability in certain measurements. SAS offers procedures for discovering the sources of variability for an outcome. Continuing with our clinical study example, we would like to know if patient weight significantly varies among the 12 clinics participating in the TIAD project. You would expect similar distributions in weight across clinics because the study entry criteria have beginning weight requirements. However, you have learned that some of the clinics did not train staff well enough to follow the study protocol where weight measurement was concerned. A box plot for weight by clinic ...

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