A treatment group would take aspirin regularly and a control group would take a placebo regularly. The heart attacj incidence in the two groups would be compared after several years. Notice that this study may be unethical because one group would have to be denied a potentially beneficial substance. Unit 2B 7. For example, this process would favor unemployed or partially employed people.
People can answer a question about beer at any time of day.
Nevertheless the study is biased. Unit 2C 7c. Clearly there is an upward trend in the data, as the percentage of percentage of full-time women workers increases with time. Visually there does not seem to be a correlation between voter turnout and unemployment.