Problem: Healthy diet and cataracts. The relationship between healthy diet and prevalence of cataracts was assessed using a sample of 1808 participants from the Women's Health Initiative Observational Study. Having a high Healthy Eating Index score was the strongest predictor of a reduced risk of cataracts, among modifiable behaviors considered. The Healthy Eating Index score was created by the U.S. Department of Agriculture and measures how well a person's diet conforms to recommended healthy eating patterns. The report concludes: "These data add to the body of evidence suggesting that eating foods rich in a variety of vitamins and minerals may contribute to postponing the occurrence of the most common type of cataract in the United States."9
Required:
(a) Explain why this is an observational study rather than an experiment.
(b) Although the result was statistically significant, the authors did not use strong language in stating their conclusions, using words such as "suggesting" and "may." Do you think that their language is appropriate given the nature of the study? Why?