Issues in Designing Controlled ExperimentsExperimental UnitsTreatments/ConditionsAssignment of Units to TreatmentsOther IssuesIssues in Designing Controlled ExperimentsExperimental Units•Items that to be used in experiment should be representative of the population of interest.–Insects/Animals/Plants of a particular gender/species/maturity–Patients with a given condition and age/size status–Primary household shopper for families of a particular size/socio-economic status–Steel rods of a specified length/radiusTreatments/Conditions•Should represent all possible levels that can provide insight to research problem–Compare 4 widely used varieties of fertilizer–Compare positive and negative valence in risk preference experiment.– Compare a new test drug with currently available standard (not ethical to include placebo)–Compare 5 distinct heating temperatures in cooking optimization studyAssignment of Units to Treatments•When no external information is available or units are homogeneous, assign them at random to treatments using random mechanism. COMPLETELY RANDOMIZED DESIGN•When external information is available, units can be lumped into homogeneous blocks and randomized to treatments within blocks RANDOMIZED BLOCK DESIGNOther Issues•Blinding: Whenever possible, subjects and researchers making measurements should be unaware of which treatment subject was exposed to.•Crossover Designs: When subjects can be assigned to all treatments in a study without affecting subsequent measurements, subjects can act as blocks. They should receive the various treatment conditions in random order with sufficient time between exposures.–Bicyclists endurance at multiple caffeine doses–Bioavailabilty studies of various drug formulations in people•Repeated Measures: Many studies measure the same subjects under a single condition at multiple time
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