Homework answers / question archive / George Washington University PUBH 6003 1)In 2007, investigators started a study of the association of cholesterol levels and stroke in a group of 2000 health care personnel who had participated in a cholesterol screening program in 1997 (20 years before the study was conducted)

George Washington University PUBH 6003 1)In 2007, investigators started a study of the association of cholesterol levels and stroke in a group of 2000 health care personnel who had participated in a cholesterol screening program in 1997 (20 years before the study was conducted)

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George Washington University

PUBH 6003

1)In 2007, investigators started a study of the association of cholesterol levels and stroke in a group of 2000 health care personnel who had participated in a cholesterol screening program in 1997 (20 years before the study was conducted) . The investigators determined (step 1…) exposure categories using cholesterol levels in all persons that were measured at the time of the screening program. A cutoff value of 200 mg/dL was used to define “high” cholesterol while those with levels below 200 were identified as having “low” cholesterol. Using this definition, 1,000 persons had “high” cholesterol levels while the remaining 1000 persons had “low” cholesterol. The investigators determined (step 2…) that 150 cases of stroke occurred by the end of 2007, with 113 cases occurring in the high cholesterol group. What is the study design that the investigators used? If they had done started this study in 1997, it would have been prospective but the numbers would have been the same. On the other hand if they had designed this study in 1997 maybe they would have used some better measure of cholesterol or measured other potential risks and confounders –now they are stuck with the measures and sample already used.

 

A.            Case-control study

B.            Retrospective cohort study

C.            Prospective cohort study

D.            Cross-sectional study

E.            Randomized clinical trial

 

 

2.            What type of risk measure of association should the investigators calculate?

 

A.            Odds Ratio

B.            Prevalence rate

C.            Interaction ratio

D.            Positive predictive value

E.            Relative risk

 

3.            Using the reported study data, what is the estimate of the risk measure that was chosen?

 

A.            3.1

B.            3.3

C.            67%

D.            1.0

E.            0.3

 

 

Select the appropriate study design from the list below that best describes the studies in Questions 4 – 6:

 

A.            Retrospective cohort study

B.            Cross sectional study

C.            Ecologic study

D.            Nested case-control study

E.            Case-crossover study

 

4.                E          A study was designed to evaluate whether the risk of having an acute

myocardial infarction (AMI or heart attack) is triggered by physical exertion and is affected by ambient temperature and whether it takes place indoors or outdoors. The study population consisted of hospitalized 24-hour survivors of an AMI who were 25-74 years of age. Data on symptoms in connection with the AMI as well as socio-demographic characteristics, medical history and smoking status were routinely collected for all participants. Patients were interviewed about their activities on the day of their AMI and the preceding 3 days using a standardized questionnaire. Activities during the hazard period (immediately preceding the AMI) were compared with activities occurring in 2 control periods, 24 and 48 hours earlier.

ANS:  The case is their own control

 

5.                B         A study was designed to determine the role that senior citizen centers play in

decreasing depression in community-dwelling older persons. A non-probability sample of older adults who live in Sebastian County, Arkansas and who attend one of the nine senior centers was selected for study. A questionnaire was administered to 257 participants asking questions about age, living arrangements, gender, and social networks. A Geriatric Depression Scale (GDS-15) was also administered to measure clinically significant depressive symptoms.

ANS:  Note exposures and outcome all present at same moment in each individual–don’t know which came first, don’t know when depression developed (or past history of depression). Since depression can be transient does that make this design more or less appropriate?

 

 

For Questions 7 – 10, match the following terms with the correct description.

 

A.            Masking or blinding

B.            Intention-to-treat

C.            Factorial design

D.            Equipoise

E.            Placebo

 

 

7.      E    An inert medication or procedure that is intended to give participants in an experimental study the perception that they are receiving treatment.

 

 

8.      D   A state of genuine uncertainty about the benefits or harms that may result from each of two interventions.

 

 

 

 

9.                C                         An experimental study that allows one to examine simultaneously the effects of multiple independent variables and their degree of interaction.

 

10.                         B             After randomization, all patients allocated to each arm in a experimental trial are analyzed together as representing that treatment or intervention group, whether or not they completed or were compliant with the intervention.