Posted: December 9th, 2014

Match the following methods for minimizing chance, bias, and confounding in an experimental study. (1 point each)

Blind
Randomization
Increase sample size

Chance

Bias

Confounding

Part 2: For each of the following statements, indicated whether the statistical association is likely a result of chance, bias or confounding and provide a brief explanation. (2 points each)
A case-control study found a positive association between self-reported chest radiographs during pregnancy and breast cancer.
Likely Cause:

Brief Explanation:                          _______________________

______________________________________________________________________

A case-control study showed a strong association exists between birth order and Down syndrome.
Likely Cause:

Brief Explanation:                          _______________________

______________________________________________________________________
A randomized clinical study found that participation in a health education program to reduce smoking initiation versus not participation in the study did not significantly reduce smoking cessation. The risk ratio was <1 but the confidence interval was very wide and included 1. (RR= 0.35; 95% confidence interval 0.14-55.01).
Likely Cause:

Brief Explanation:                          _______________________

______________________________________________________________________
A hospital-based case-control study identified a strong association between oral contraceptives and blood clots. Many doctors suspected the association and hospitalized some women who used oral contraceptives for evaluation.
Likely Cause:

Brief Explanation:                          _______________________

______________________________________________________________________
Part 3: Identify the following studies as either case-control, retrospective cohort, or prospective cohort (1 point each).
Vietnamese Experience Study: Subjects were several thousand soldiers stationed in Vietnam from 1969-1971 and several thousand soldiers stationed in Europe form 1969-1971. In 2000, investigators initiated a study to determine and compare the death rates and prevalence of illness in both groups.

13.    Subjects were persons with laboratory confirmed Campylobacter jejuni infection and one healthy friend of each. All subjects were asked about their consumption of meat, poultry and milk products.

In 1948, researchers recruited 5,209 men and women between the ages of 30 and 62 from the town of Framingham, Massachusetts, and began the first round of extensive physical examinations and lifestyle interviews that they would later analyze for common patterns related to CVD development. Since 1948, the subjects have continued to return to the study every two years for a detailed medical history, physical examination, and laboratory tests.

Part 4: For each of the following list whether the risk ratio will be equal to one, greater than one, or less than one (1 point each).
15.    Exposure is associated with decreased risk of disease: ______________________
16.    Exposure is associated with increased risk of disease: _______________________
17.    There is no association between exposure and disease: ______________________

Part 5: Read each of the following studies, construct the appropriate 2×2 table, calculate the measure of association, state the study design, and state the interpretation of the results. (4 Points for each scenario.)
An investigator wanted to determine whether playing video games constantly (chronic videogamer: CVG) was associated with carpal tunnel syndrome (CTS). By interviewing males ages 15-30 in a Midwestern city, the researchers located 550 males with CTS. A total of 600 additional males without CTS were selected at random and interviewed. Of those with CST, 84 reported not being a CVG. A total of 365 control males reported being a CVG. (1) Identify what type of study this is (2) Construct the appropriate 2×2 table regarding chronic videogaming and carpal tunnel syndrome (3) Calculate the odds ratio between chronic videogaming and carpal tunnel syndrome and (4) Interpret the results.

A group of 1,000 female college seniors from a large Midwestern university were followed for 20 years to investigate whether the use of oral contraceptive increases women’s risk of developing blood clots. Of these females, 550 were oral contraceptive users and at the end of 20 years, 48 had developed blood clots. Among those not using oral contraceptives 17 developed blood clots. None of the females had clots when the study began. (1) Identify what type of study this is (2) Construct the appropriate 2×2 table regarding the use of oral contraceptives and the development of blood clots (3) Calculate the risk ratio between the use of oral contraceptives and the development of blood clots and (4) Interpret the results .

Part 7: Identify the following features with appropriate study design:
Case-control study
Cohort study

Categorize subjects on the basis of exposure and then follow up to see if they develop the health condition we are studying.

Generally used to explore rare diseases.

Useful for exploring several risk factors for a given outcome.

After some time compare the disease rate for the exposed with that of the unexposed.

Generally used when the exposure is rare.

Useful when there are several outcomes related to a given exposure.

Enrolls a group with disease and an appropriate group without disease and compares their patterns of previous exposures.

Part 8: Match the sources of bias with the type of study design and the best way to minimize the bias.

Type of study design:
Case-Control
Cohort

Way to minimize bias
Obtain controls from the same work environment as cases
Obtain controls from the general population.
Incentives
Take steps to assure that mild, clinically resolved or fatal cases are represented in the case group
Refer to medical records containing exposure information if they exist

Study Design            Way to minimize bias

33–34    Loss to follow-up                    _________

34–35    Recall, interviewer                    _________

36–37    Healthy worker effect                    _________

38–39     Berkson’s bias                    _________

40–41     Neyman’s bias                    _________

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