HOMEWORK3

Wednesday, December 3, 2014 at 11pm

NAME____________________________________

Please type your responses to each of the questions and then save your responses as a Word document (or Word compatible document) called, “Your Name HW3.doc”. Upload your homework on Blackboard in the “Assignment submission blog.” Only the student who uploads the document and the instructors will have access to the file. Blackboard will automatically include the time the file was uploaded.

To upload a document on Blackboard:

Click on “Assignments”.

Click on “new entry” on the right hand panel under “Actions’”

Next click on the button for ‘Upload file’. It is the third button from the left on the bottom toolbar (picture of a piece of paper with a green arrow pointing upward).

Click on the ‘browse’ button to find the folder where you saved your homework file and the file itself. Click on your file.

Finally hit the ‘Upload’ button and then insert. You will see that it has been uploaded into your blog as a hyperlink.

After you upload your assignments, go to My Grades to make sure you see a green exclamation point which will confirm that your assignment has successfully uploaded.

If Blackboard is down when you submit your assignment, be sure to email your document to both instructors before the deadline date and time.

You may confer with fellow students on this homework (working in groups can be helpful). However, all of your written responses must be written using your own words.

Grade:

Part 1: ___ out of 42

Part 2: ___ out of 36

Part 3: ___ out of 22

(Extra Credit ___ out of 4)

Total: ___ out of 100

PART 1: Multiple Choice (Questions 1-14): Unless otherwise indicated, choose the ONE best answer. Type your answer below each question. (3 points each; 42 points total)

Questions 1-2. Suppose researchers are conducting a case-control study of whether physical fitness is a protective factor against heart attack. Cases are persons newly-admitted to the coronary care unit at area hospitals. Controls are obtained through random-digit dialing in that same geographical area. The research staff hypothesizes that physical fitness is protective against heart attacks. When asking the controls about the history of physical fitness, they make sure to probe them very carefully, whereas they do not do the same with cases, in part so they will not be burdened given their condition.

1. Given this scenario, what type of bias may affect your results? Select the one best answer.

a. recall bias

b. information bias

c. selection bias

d. participation bias

2. This bias may affect your results by:

a. Finding less of a protective effect from physical fitness

b. Finding a greater protective effect from physical fitness

c. Introducing confounding into the relationship

d. Introducing random error into the relationship

Identify the Role of the Third Variable

For questions 3-5, choose which of the following best describes the third variable (i.e. the variable other than the exposure and the outcome) based on the study results and/or description of the researchers’ theory.

A. Confounder

B. Mediator

C. Effect modifier

3. Using data from a case-control study, researchers evaluate the association between a history of obesity as measured by BMI and a type of esophageal cancer (adenocarcinoma). They find that obese men have 2.6 times the odds of developing esophageal adenocarcinoma compared to non-obese men. They then hypothesize that obesity causes an increased risk of gastric reflux, which is a risk factor for esophageal adenocarcinoma. Once they adjust for gastric reflux, they find that obese men have 1.3 times the odds of developing esophageal adenocarcinoma compared to non-obese men. In this scenario, what is the third variable, gastric reflux, likely to be?

4. Researchers conduct a case control study to look at the association between cell phone

usage (exposure) and brain cancer (outcome). They find, overall, people who use a cell phone

regularly have 2 times the odds of having brain cancer compared to people who do not use a

cell phone regularly. Once they adjust for age, they find that people who use a cell phone

regularly have 3 times the odds of having brain cancer compared to people who do not use a

cell phone regularly. In this scenario, what is the third variable, age, likely to be?

5. Researchers conduct a cohort study in Southern Africa to look at the association between attending school and HIV infection in youth. Overall, they find a slightly protective relationship between attending school and HIV risk (RR=0.95). However, after stratifying on gender, they find that attending school for women is strongly protective (RR=0.6) against the risk of HIV, whereas the risk of HIV is slightly increased among men who attend school (RR=1.3 ). In this scenario, what is the third variable, gender, likely to be?

Questions 6-9: A study was conducted to look at the association between maternal consumption of water contaminated with manganese during pregnancy, and pediatric impaired motor development at age 4. Manganese is a metal often found in water from very deep wells.

You are concerned that people who can afford to have deep wells dug (those exposed) may be wealthier, and therefore they may have better nutrition during pregnancy. Poor prenatal nutrition has been implicated as a risk factor for numerous neurological diseases. Expectant mothers were interviewed about their manganese exposure and their newborn offspring were followed from birth through age 4 to determine if mothers, who consumed water with manganese during pregnancy, were more likely to have offspring with motor development impairment as compared to mothers who did not consume water with manganese during pregnancy. The resulting data are below in tables 1a and 1b. Use this information to answer questions 6-9:

Table 1a. Crude Analysis: Association between maternal consumption of contaminated water and incidence of pediatric impaired motor development

Motor Development Impairment (D+)

Healthy (D-)

Total

Manganese exposure(E+)

107

156

263

No manganese exposure

(E-)

85

528

613

Total

192

684

876

Table1b. Stratified Analysis: Association between manganese exposure and incidence of pediatric motor development impairment, stratified by nutrition

Good Nutrition

Poor Nutrition

Manganese exposure

Motor Development Impairment (D+)

Healthy (D-)

Total

Motor Development Impairment (D+)

Healthy (D-)

Total

Yes (E+)

10

45

55

97

111

208

No (E-)

35

173

208

50

355

405

Total

45

218

263

147

466

613

Odds Ratio

1.1

3.8

6.What type of epidemiological study design is this?

a. Case-control study

b. Cohort study

c. Randomized control trial

d. Ecological study

7. Using the results of the crude analysis (Table 1a), what is the unadjusted odds ratio for the association between maternal manganese exposure and pediatric motor development impairment?

(107X528)/(156X85) = 4.26

(107 x 156)/(85 x 528) = 0.37

(107/263)/(85/613) = 2.86

(170*263)/(85*613) = 0.86

8. Assuming that poor nutrition is NOT on the causal pathway between manganese and motor development impairment, what might your temporarily conclude before you run additional analyses?

Nutrition appears to act as a mediator in the association between manganese and motor development impairment

Nutrition appears to act as an effect modifier (interaction term) in the association between manganese and motor development impairment

Nutrition influenced the response about manganese exposure and led to information bias.

Nutrition appears to be confounding the association between manganese exposure and impaired motor development.

9. Based on the study results, what measure of association would you report to best describe the association between manganese exposure and motor development impairment?

The crude odds ratio

The odds ratios stratified on nutrition

The adjusted odds ratio, adjusting for nutrition

None of the above

10. Researchers conduct a study on adults over the age of 45 to determine whether an association exists between meditation sessions and heart disease. They report that those who engage in daily meditation sessions have a relative risk of 0.6 in developing heart disease over 10 years as compared to those who do not engage in daily meditation sessions. The 95% confidence interval had a range from 0.5 to 1.6. Select the correct statement solely based on the information provided in this scenario:

a. The authors should fail to reject the null hypothesis.

b. A Type I error could have occurred.

c. The study had sufficient power to detect a true difference of at least 0.6.

d. The researchers are confident that daily mediation sessions would protect against heart disease in at least 95 out of 100 studies, if conducted similarly.

e. The authors should have reported a 90% confidence interval to obtain statistical significance.

11. A study was conducted of the reliability of two different radiologists’ readings of lung x-rays for the diagnosis of pneumonia. Each of the two radiologists read the same 150 X-rays and classified each X-ray as ‘Pneumonia’ or ‘Not pneumonia’. The investigator reported a kappa statistic=0.71. Which of the following is true about this result?

a. A kappa statistic of 0.71 shows a poor agreement between the two radiologists beyond what is expected by chance alone.

b. Kappa is the wrong statistical test to run in this case.

c. A kappa statistic of 0.71 shows a good agreement between the two radiologists beyond what is expected by chance alone.

.

12. Recall bias occurs when:

a. Researchers in a case-control study ask more probing questions of cases than controls.

b. Researchers are not blinded and they recall which subjects were cases and which

subjects were controls.

c. Subjects in one arm of a randomized controlled trial recall their treatment compliance

better than subjects in the other arm of the randomized controlled trial.

d. Cases and controls in a case-control study differentially report their exposure histories because they know their disease (outcome) status.

13. The researchers recommend vaccinating girls ages 11-14 years in order to vaccinate girls

prior to sexual initiation. The US Food and Drug Administration (FDA) approves the vaccine

for girls/women aged 15 years and over, but does not recommend its use in girls under age

15 without additional RCTs that have enrolled younger girls. In this scenario, what is the US

FDA concerned about?

A. Presence of confounding

B. Presence of information bias

C. Lack of external validity

D. Lack of internal validity

14. Select the correct statement concerning effect modification (interaction):

a. If the authors report that gender is an effect modifier in their study, they

should adjust for gender.

b. Effect modification introduces error and can invalidate a trial’s result.

c. Matching is the best way to address effect modification in a prospective cohort

study.

d. If effect modification is present, it suggests that the association between exposure and disease differs according to a third factor.

e. If the crude risk ratio in a study is 2.0, and the stratum –specific risk ratios for gender are 1.4 for men and 1.3 for women, gender is probably an important effect modifier in the study.

Part 2: Short Answer (Questions 15-21): Answer the following questions using full sentences. Be as specific as possible for full credit and answer the questions in your own words. (36 points total)

15. In a case control study of the association between chewing tobacco and oral cancer, you

think that individuals with oral cancer are more likely to truthfully report that they chewed

tobacco than controls.

a. What type of misclassification is this? Be sure to state whether it is differential or non-differential, AND whether it is misclassification of the exposure or the diseasein your

response. Justify your response. (4 points)

b. How would this misclassification bias the OR you calculate using your study findings?

Be sure to state whether you think it would bias the OR toward or away from the null

value of 1 in your response. (3 points)

16. You decide to implement a cohort study that evaluates the association between sleeping less than 6 hours a night and reported levels of daily stress, but you are worried that the results from your observational study will be confounded by age.

Describe the entire criteria that age must fulfill to be a potential confounder. (3 points)

17. Name and describe 1 way you could attempt to control for confounding by age during the study design phase (3 points) and describe one drawback/weakness of that method. (2 points)

18. An investigator conducted a cohort study to investigate the relationship between post-traumatic stress disorder (PTSD) and subsequent stroke. The crude RR was 3.5, but after adjusting for frequent migraine headaches, the RR was 1.6. Assuming you have determined that migraine headaches are NOT an effect modifier can you determine from these data results alone whether the headaches are a confounder or mediator? Why or why not? Please describe what you need/must do to reach a conclusion. (4 points)

19a-c. The randomized control trial (RCT) is considered the “gold standard” of study designs, with a cohort study coming in a distant second. Compare the RCT to the cohort study design. (6points total)

Specifically:

a. Describe one problem that a RCT addresses that a cohort study does not (2 points)

b. Describe one problem that both study designs share (2 points)

c. Describe one condition where a cohort study might be preferable (2 points)

20. A case-control study of lung cancer and occupation was conducted among men living in Hyderabad, a city in India. It identified excess risk of lung cancer among various occupations, including filling station attendants, bus drivers, and barbers. (1) Define external validity (3 points) and (2) State whether or not there would be good external validity of these findings and be to provide several sentences to support your opinion. (4 points)

21. A cohort study investigating the association between exposure to motor vehicle pollutants (specifically nitrogen dioxide) and development of lung infection will be conducted by the Environmental Protection Agency (EPA).

(a) Write down the null and alternative hypothesis (2 points) that will be tested, and (b) in the context of this example, state what a Type I and Type II error would be (4 points)?

PART 4 – OPTIONAL EXTRA CREDIT (4 points total)

Questions 23a & b.

23a. In studies that have selected alpha=0.05 as the probability level at which they are willing a type I error to occur, which of the following results would be interpreted as statistically significant? (CIRCLE ALL THAT APPLY) . (2 points)

23b. Which of the results with confidence intervals above is most precise? List the most precise confidence interval and explain why it is most precise.(2 points)Click here to have a similar paper done for you by one of our writers within the set deadline at a discounted