A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness, researchers placed an ad online asking for volunteers to participate in the study. One hundred subjects replied and were informed that one group would receive the new cream and the other would receive a cream with no active ingredient. All 100 subjects were exposed to poison ivy. Fifty were then randomly assigned to the group with the new cream, and 50 were randomly assigned to the group with the cream with no active ingredient. After three days, the subjects’ level of irritation was measured.
A community is considering raising funds to pay for improvements to the community swimming pool. To measure the level of interest, community leaders survey patrons of the community pool on a Saturday afternoon. Of the 103 patrons surveyed, 87 approve of raising funds to pay for improvements. Which of the following is a true statement regarding the design and results of the survey?
Race organizers want to survey the participating runners on the quality of the running course. Which of the following uses systematic random sampling?
A restaurant chain would like to measure the proportion of customers who are generally satisfied with the service provided by its staff. At the end of the meal, as the check is delivered to the table, the server asks those at the table to rate their satisfaction with the service provided as "Very Satisfied,” "Satisfied,” or "Not Satisfied.” During a one-week period, 147 customers were surveyed and 135 (93%) reported they were either Satisfied or Very Satisfied. How might the results be biased in obtaining an estimate of all customers who are satisfied with service?
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