A 71-year-old man comes to the office due to slowly progressive shortness of breath for the past year. He enjoys working in his garden, but shortness of breath has forced him to reduce the time he spends there. He also has a mild morning cough productive of whitish sputum. He estimates that his physical activity level is 65 with chronic obstructive pulmonary disease in the study completed all the surveys and questionnaires. Which of the following best explains the potential bias introduced by the nonresponse in the study? A)Compared to respondents, nonrespondents represent an entirely different population B)Nonrespondents caused a violation of the assumption of independence between observations C)Nonrespondents reduced the sample size; therefore, the likelihood for type I error is increased D)Respondents and nonrespondents come from the same population; therefore, the potential for bias is minimal E)Respondents may differ in some important way from nonrespondents

Question

A 71-year-old man comes to the office due to slowly progressive shortness of breath for the past year. He enjoys working in his garden, but shortness of breath has forced him to reduce the time he spends there. He also has a mild morning cough productive of whitish sputum. He estimates that his physical activity level is <30 min/day. The patient has a history of hypertension. He is a retired middle school teacher. He smoked 2 packs of cigarettes daily for 20 years and quit 15 years ago. Blood pressure is 127/85 mm Hg, pulse is 78/min, respirations are 14/min, and pulse oximetry is 93% on room air. BMI is 24 kg/m². Occasional end-expiratory wheezes are present on lung examination, and the heart examination demonstrates a regular rate and rhythm. Chest x-ray shows hyperinflation, and pulmonary function test results are consistent with an obstructive defect. Suppose that 115 of the 160 (71.9%) patients age >65 with chronic obstructive pulmonary disease in the study completed all the surveys and questionnaires. Which of the following best explains the potential bias introduced by the nonresponse in the study? A)Compared to respondents, nonrespondents represent an entirely different population B)Nonrespondents caused a violation of the assumption of independence between observations C)Nonrespondents reduced the sample size; therefore, the likelihood for type I error is increased D)Respondents and nonrespondents come from the same population; therefore, the potential for bias is minimal E)Respondents may differ in some important way from nonrespondents

Quizplus · Accepted Answer

Explanation: Nonresponse bias may occur when a proportion of study participants become nonrespondents. Nonresponse typically affects studies that use questionnaires or surveys to collect data from participants. Although respondents and nonrespondents come from the same sample of participants, they may or may not represent the same population. Therefore, nonresponse may potentially bias a study if nonrespondents are systematically different from respondents in important characteristics (eg, exposure or disease status) that the study is designed to identify. If researchers determine that respondents do not differ in meaningful ways from nonrespondents with regard to exposure or disease status, then nonresponse only reduces the sample size of the study. This leads to an increased probability of a type 2 error (probability of failing to reject a false null hypothesis [false negative]) and reduced statistical power. (Choices A and D) Depending on whether respondents differ in meaningful ways from nonrespondents, they may or may not come from the same population. This example does not provide enough information to establish whether respondents differ from nonresponders. (Choice B) The assumption of independence between observations is a foundation for many statistical tests. It states that the value of one data point (observation) does not depend on the value of any other data point. In this example, nonresponse has no bearing on the assumption of independence of observations. (Choice C) The probability of a type I error (rejecting a true null hypothesis [false positive]) usually increases as sample size increases, and not as sample size decreases due to nonresponse. Educational objective: Nonresponse increases the potential for bias in 2 different ways: it introduces a bias in estimates when nonrespondents differ from respondents in the outcome of interest; and it contributes to a decrease in statistical power given that the sample size has been reduced. However, a significant nonresponse rate in a study does not necessarily translate into bias.

A 71-Year-Old Man Comes to the Office Due to Slowly