In an experiment to measure the effect of fluoride “varnish” on the incidence of tooth cavities, thirty-four 10- year-old girls whose parents volunteered them for the study were randomly assigned to two groups. One group was given fluoride varnish annually for 4 years, along with standard dental hygiene; the other group followed only the standard dental hygiene regimen. The mean number of cavities in the two groups was compared at the end of the 4 years.

a. Are the participants in this experiment subject to the placebo effect? Explain.

b. Describe how you could alter this experiment to make it doubleblind.

c. Explain the purpose of the random assignment in this experiment.