DescRiPTive STATISTICS Identifying confounders and ways to eliminate them in an... V A medical researcher is interested in studying the possible relationship between BMI (body mass index) and cancer. To investigate, the researcher conducts an observational study by reviewing a samp|_e of 550 medical records of male adults. From the medical records, he gathers the following information for each participant: whether or not the participant hasfhad any type of cancer, the participant's BMI, and the participant's nutritional habits. From the results, the researcher creates two groups: hasfhad cancer (HC) and never had cancer (NHC). Then he compares the average BMI between the two groups. (a) why might the researcher have chosen to perform an observational study (by reviewing medical records) and not a randomized experiment (by assigning participants to either the HC or NHC group at random)? Choose the best answer from the choices below. 0 A randomized experiment should never be performed when it is possible to perform an observational study. When groups are randomly assigned, the researcher cannot control the types of participants in each group, making the results of a randomized experiment unreliabie. O For a randomized experiment to be performed, the researcher must ask people in the mpulation to voiunteer to take part. This would mean that there would not be any chance to include people who havefhad cancer in the sample. C) For a randomized experiment to be performed, the researcher would have to randomly assign participants to either the HC or the NHC group. But whether or not a person has cancer is out of the researcher's control. (b) The variable biological sex is not a possible confounder in this study. Choose the best reason why. 0 A variable is a confounder it, based on its value, it prohibits some members of the sample from participating in the study. For this study, all of the participants in the sample were male. 50, each person in the sample could participate since they DE scmpnvc STATISTICS Identifying confounders and ways to eliminate them in an... V (b) The variable biofogfcal sex is not a possible confounder in this study. Choose the best reason why. 0 A variable is a confounder if, based on its value, it prohibits some members of the sample from participating in the study. For this study, all of the participants in the sample were male. 50, each person in the sample could participate since they could be placed into one of the two groups. 0 A variable is a confounder if its effect on the outcome cannot be distinguished from the effect on the outcome from different treatments. (In our context, the outcome is BMI, and the treatments are hasfhad cancer and never had cancer.) In this study, both treatment groups (NC and NHC) were similarly comprised of only male participants. Thus, the researcher designed the study so that a participant's biological sex would not be a confounder. (c) The variable nutritional habits is a possible confounder in this study. Choose the best reason why. 0 A variable is a confounder if its effect on the outcome cannot be distinguished from the effect on the outcome from different treatments. (In our context, the outcome is BMI, and the treatments are hasfhad cancer and never had cancer.) There is already a noticeable difference between the two groups of participants in terms of having cancer. It's possible the participants in the HC group differ from the participants in the NHC group in other characteristics, such as nutritional habits, making it difficult to detem'iine which variable is affecting BMI. O A variable is a confounder if, based on its value, it prohibits some members of the sample from participating in the study. For this study, there may be some participants who had extremely healthy nutritional habits making it not possible for them to participate. DE scniPTive STATISTICS Identifying confounders and ways to eliminate them in an... (d) Suppose the researcher is interested in reducing the effect that differences in nutritional habits might have on the BMI between the cancer and cancerfree groups. what is a reasonable approach for the researcher to take? Choose the best answer from the choices below. 0 The researcher could divide the participants in the cancer group into two groups: participants with good nutritional habits and participants with poor nutritional habits. The same division would be done in the never had cancer group. Then she could compare the average BMI between the two groups, by level of nutrition. m 0 The researcher could aim to select a participant with cancer who has poor nutritional habits and then find a participant who has never had cancer with good nutritional habits. She could continue to create pairs of participants in this wayr such that each pair contained one cancer participant with poor nutritional habits and one participant who has never had cancer and has good nutritional habits. Then she could compare the average BMI between the group of participants with cancer (having a poor nutritional habits) and the group or participants who have never had cancer (having a good nutritional habits). IKIIEEEI O The researcher could increase the sample size. IncreaSing the sample size helps to reduce the effect that confounding variables have on the outcome of the study. Because there are so many different possible ages, it would be necessary to have a sample size much larger than 550 adults in order to have enough variety for a reasonable study. DESCRlPTIVE STATlSTICS Understanding the differences between designed experiments... V Boris is teaching a math course to 170 incoming students. He is interested in comparing his effectiveness teaching this course using activityebased learning to his effectiveness teaching this course using textbook presentation. He gives each of his students a pretest and forms two groups of 85 students each. To help make sure that the groups are similar in composition with respect to factors such as age, math ability, and test anxiety, the students are randomly assigned into the two groups. One of the two groups is randomly a55igned to be taught by Boris using the activitybased learning approach for the duration of the course, and the other group will be taught by Eons using textbook presentation for the duration ofthe course. At the end of the course, Boris will test all of the students again with a posttest. and he will examine the increase in test score from the pretest to the nosttest for each group. (a) First choose whether the procedure described above is an observational study or a designed experiment. Then further categorize the procedure by choosing the correct type of observational study or designed experiment. O Observational study 0 Designed experiment 0 prospective O doubleblind O retrospective 0 completely randomized (b) which one of the following best describes the explanatory (independent) and response (dependent) variables? 0 The explanatory variable is the teaching approach and the response variable is the math ability. 0 The explanatory variable is the math ability and the response variable is the increase in test score. 0 The explanatory variable is the increase in test score and the response variable is the teaching approach. 22' MtGraw Hill LLC. All Right: Fit-served If :jj: DESCRIPTIVE STATISTICS Understanding the differences between designed experiments... V (b) which one of the following best describes the explanatory (independent) and response (dependent) variables? 0 The explanatory variable is the teaching approach and the response variable is the math ability. 0 The explanatory variable is the math ability and the response variable is the increase in test score. 0 The explanatory variable is the increase in test score and the response variable is the teaching approach. 0 The explanatory variable is the teaching approach and the response variable is the increase in test score. (c) Suppose there was no significant difference in the test score increases between the activitybased learning approach and the textbook presentation approach. Does Boris have reason to conclude that a student's age has no effect on that student's test score? Choose the best answer below. 0 Yes. Since there was no Significant difference in the test score increases between the two approaches, the procedure has proved that no variable affects the test scores. 0 Yes. Since the composition of the two groups was similar with respect to age, Boris has reason to make this conclusion. 0 No. Based on the design of the procedure, Boris has no reason to make this conclusion. I 202" McGra'riI-lill LLCI All Fights. FEE-served. _T