This topic is taught through its practice: 12 practice questions, each with the reasoning behind the answer, and the same idea again in plain words.
Quick check
5 questions here, of 12 in this lesson’s practice set. Answers stay hidden until you check.
Question 1 of 5foundational
During data collection, a research scale is checked against a certified 50 kg calibration weight and displays 51 kg on all ten checks. Because the error is the same size and in the same direction every time, it is systematic error (bias) rather than random error. What is the size of the systematic error, in kilograms?
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Question 2 of 5foundational
A trial of a fall-prevention program enrolls 300 residents at a single retirement community; 285 of them are women and the average age is 82. The study is well randomized and carefully controlled, so internal validity is strong, but the makeup of the sample limits external validity (generalizability). What percentage of the enrolled sample is female?
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Question 3 of 5foundational
A questionnaire about workplace stress is mailed to 500 nurses, and 150 usable surveys are returned. Nonresponse bias becomes a concern when the people who do not answer differ systematically from the people who do. What is the nonresponse rate for this survey?
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Question 4 of 5intermediate
In an observational study, the crude risk ratio linking a dietary supplement to respiratory infection is 2.4. After adjusting for participants' baseline exercise habits, the risk ratio falls to 1.2. The change-in-estimate approach quantifies confounding as percent change = (crude - adjusted) / adjusted x 100, reported as an absolute value. What is the magnitude of confounding by exercise habits?
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Question 5 of 5intermediate
A 12-week trial enrolls 240 participants in the intervention group and 240 in the control group. By week 12, 36 participants have withdrawn from the intervention group and 12 from the control group. Differential attrition threatens internal validity because the remaining groups may no longer be comparable. How many percentage points higher is attrition in the intervention group?
