Issues in Designing Controlled Experiments - PowerPoint PPT Presentation

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Issues in Designing Controlled Experiments

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... treatment conditions in random order with sufficient time between exposures. ... measure the same subjects under a single condition at multiple time points ... – PowerPoint PPT presentation

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Title: Issues in Designing Controlled Experiments


1
Issues in Designing Controlled Experiments
2
Experimental 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/radius

3
Treatments/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 study

4
Assignment 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
    DESIGN

5
Other 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 points
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