A researcher would like to investigate whether people suffering from insomnia can be helped by taking yoga classes.She designs an experiment as follows.She will obtain a group of volunteers who are suffering from insomnia and who do not currently practice yoga.Each person's degree of insomnia at the start of the experiment will be evaluated.She will investigate whether yoga classes every day or three times per week are more effective.So the factor yoga will have 3 levels (no yoga,yoga three times a week,yoga every day).Each volunteer will choose which group they would like to be part of.At the end of a suitable time period,for example two months,each person's degree of insomnia will again be evaluated.The improvement for the three groups will then be compared.The person evaluating the insomnia levels will be blinded to which group the patients were in.Identify the most serious flaw in this experiment.
A)The volunteers were not selected randomly.
B)The person evaluating the insomnia levels could have been biased.
C)There was no placebo group.
D)There was no blocking.
E)Volunteers chose their treatment instead of being randomly assigned to one of the groups.

Question

Quizplus · Accepted Answer

By allowing volunteers to choose their own treatment, there is a risk of self-selection bias. People who are more motivated to try yoga may be more likely to choose the yoga groups, while people who are skeptical or uninterested in yoga may choose the no yoga group. This could result in differences between the groups at the start of the study that could confound the results. Random assignment to groups would help to minimize this risk.

A Researcher Would Like to Investigate Whether People Suffering from Insomnia