Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in 1976. The study identified 981 women who lived near the site of the accident and were under age 40 at the time. Fifteen of the women had developed breast cancer at an unusually young average age of 45. Medical records showed that they had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer.

Read each brief report of statistical research, and identify

a) Whether it was an observational study or an experiment.

If it was an observational study, identify (if possible)

b) Whether it was retrospective or prospective.

c) The subjects studied and how they were selected.

d) The parameter of interest.

e) The nature and scope of the conclusion the study can reach.

If it was an experiment, identify (if possible)

b) The subjects studied.

c) The factor(s) in the experiment and the number of levels for each.

d) The number of treatments.

e) The response variable measured.