PUBHLTH6001_Lab6

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Ohio State University *

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6001

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Health Science

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Dec 6, 2023

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PUBHLTH 6001 Lab 6: Randomized Trials Course Learning Objectives: CLO3: Define terms, concepts, and key features of epidemiologic study designs Module Learning Objectives: Describe why randomization is useful when asking causal questions Describe why blinding is used in randomized trials Note: This lab does not require the use of Stata software. Resources: Gordis - Chapter 10 and Appel et al. article cited below. Preliminaries: Read the following article: Appel LJ, Moore TJ, Obarzanek E, Vollmer WM, Svetkey LP, Sacks FM, Bray GA, Vogt TM, Cutler JA, Windhauser MM, Lin PH, Karanja N. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336(16):1117-24. https://www.nejm.org/doi/full/10.1056/nejm199704173361601 Use this article to answer the following questions. 1. What was the purpose of the trial? Answer: The purpose of this trial was to look at 3 dietary approaches to stop hypertension by assessing the effects of dietary patterns on blood pressure. The three diets were: a combination diet (high in fruit, vegetables, low-fat dairy, and total fat, a diet high in fruit and vegetables, and a typical American control diet). 2. Losing weight causes blood pressure to drop. Why do you think the investigators made an effort to keep participants’ weight stable in this trial? Answer: If participants lost or gained weight during the trial, the results could be wrong because the blood pressure would be controlled by weight and not the diets patients were eating. The investigators tried to keep calorie intake as steady as possible for all participants to try and avoid false results. The diet needed to be an independent variable. 3. What was the purpose of randomization in this study (i.e. why is randomization done)? Answer: The purpose of randomization in this study is to ensure that the personal characteristics of each study group are similar. Randomization (in principle) will make the groups similar as regards known and unknown characteristics. The essence of good comparison is that the compared groups are the same EXCEPT for the treatment. So, in this investigation, the alternate diet and control groups need to stay the same so any Page 1 of 2
PUBHLTH 6001 differences can be attributed to diet and no other categories such as weight, age, and income. 4. How would you evaluate whether randomization “worked” or not? Answer: In this study, we need to review Table 2 to see if all three groups' participants have similar characteristics. 5. Did randomization work? Answer: Based on the answer to the prior question, I would say yes, as the key characteristics in the groups all look similar. But to know for sure, we would need to run statistical tests to see if they are significantly different. 6. In the methods section on page 1118, the authors note that staff members who took blood pressure measurements were blinded to each participant’s group assignment (i.e. whether the participant was assigned to the combination diet, the fruit/vegetable diet or the typical American control diet). Why do you think they blinded the staff members? Answer: If the staff members who took the blood pressure knew which group a participant belonged to, they could interpret the blood pressure reading they were taking favoring one way of the study. If there was no blinding and they wanted results to look better for the healthy dietary change, they could record the blood pressure lower than it actually was. By having the staff members be blinded during the study, it can help remove any bias they may have. Page 2 of 2
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