Biostatistics example problem:

The clinical trial of a polio vaccine involved 200,000 children treated with the Salk vaccine and 200,000 other children given a placebo. Only 33 of the children in the Salk treatment group later developed polio, but 115 of the children in the placebo group later developed polio.

a. Are the given values discrete or continuous?

b. Identify the level of measurement (nominal, ordinal, interval, ratio) for the numbers 33 and 115.

c. If 50 children from the treatment group are randomly selected and their average (mean) age is calculated, is the result a statistic or a parameter?

d. Identify the nature (observation/experimental) and timing of the study (retrospective/prospective). What impression do you have of the relationship between vaccine and polio (causative/associative)?