Understanding ExperimentsExampleRandom AllocationTreatment and Control GroupsRandom vs. Nonrandom AllocationResponse BiasPlacebosSlide 8Experimenter BiasDouble-Blind ExperimentsThe Placebo EffectUnderstanding ExperimentsLecture 10Section 3.5Fri, Feb 1, 2008ExampleSuppose a drug is given to 100 patients suffering from a particular disease.After 2 weeks, 90% of the patients have recovered.The researchers conclude that the drug was effective.What is wrong with this?Random AllocationThe assignment to the groups should be random (a randomized design).The subjects could be numbered 1 – 100.Then use a random number generator to obtain 50 (distinct) random numbers from 1 – 100.Those 50 subjects would be assigned to Group 1.The rest would be assigned to Group 2.Treatment and Control GroupsTreatment group.Control group.Random vs. Nonrandom AllocationWould it be wrong to allow the individuals choose whether to be in the treatment group or the control group?Would it be wrong for the researchers to decide, subject by subject, who goes in which group?Why?Response BiasAre the subjects in the treatment group aware of the purpose of the experiment?If so, will they be more likely to report feeling well?Are the subjects in the control group aware that they are not receiving the drug?If so, will they be more likely to report feeling ill?What can we do about this?PlacebosPlaceboSingle-blind experimentPlacebosEverybody in the treatment group is administered the drug.Everybody in the control group gets the placebo.The researchers look for differences in the groups’ recovery rates.Experimenter BiasExperimenter bias This is similar to response bias except that it is caused by the experimenter, not the subject.How can we control for experimenter bias?Double-Blind ExperimentsDouble-blind experimentThe Placebo EffectThe placebo effect is when a subject responds to the “treatment,” even though the treatment was only a placebo.It is difficult to control for the placebo
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