Chapter 8 Exercises  

8.1 Vitamins and neural tube defects (p. 169).  Link to article by Milunsky et al., 1989. 

8.2 Framingham men (pp 169 - 170). 

8.3 CMV and restenosis (p. 170).

8.4 Cardiac arrest during high-intensity activity (p. 170).

8.5 Hepatitis B and liver cancer (fictitious). A study of Hepatitis B infection and liver cancer found 65 cases of liver cancer in 65,000 person with Hepatitis B. In a Hepatitis-free cohort, there are 5 cases in 215,000 individuals.

(A) Calculate the RR of liver cancer in this study. Interpret this statistic. 

(B) Calculate the RD. Interpret the results. [Units are required when interpreting the rate differences.]

(C) Which of the above statistics quantifies the strength of the association? Which quantifies the effect in absolute terms?

8.6 Stress hormones and coronary disease. Psychosocial stressors stimulate the secretion of catecholamines from the adrenal glands. As part of this stress response, catecholamines stimulate the sympathetic nervous system, constrict arteries, accelerates the heart rate, and increase cardiac ejection volumes. These may have deleterious effect on heart health. In a study was conducted to determine whether high levels of endogenous catecholamines increase the risk of coronary heart disease, 609 coronary heart disease free white males with high catecholamines levels had 76 coronary incidents. In contrast, 487  males with low catecholamines levels experienced, 44 incidents (Cassel, 1971). Calculate the relative risk of coronary disease associated with high catecholamine levels.  Interpret this finding.

8.7 Old hat. John Snow (1855) compiled the following information during his investigation of the London 1854 cholera outbreak.

Water Source

Cholera deaths

No. of households

Southwark & Vauxhall Co.

1263

40,046

Lambeth Co.

98

26,107

 

(A) Calculate the cholera mortality rates by water source per 1000 household.

(B) Calculate the risk difference associated with the Southward & Vauxhall Company water source.

(C) Comment on your findings.

8.8 Joseph Goldberger. In 1918, Joseph Goldberger (1874 - 1929) wrote "of the 127 households owning cows which supplied milk during the three months preceding the date of the canvass in the spring of 1916, two ... were pellagrous; whereas of 451 not owning such cows, forty-seven ... had one or more cases of pellagra." Let "not owning a cow" be the risk factor. Calculate R1, R0, RD, and RR.

8.9 Zocor. A randomized clinical trial evaluated the cholesterol-lowering drug Zocor on heart attack risk (4S Study Group, 1994). The treatment group of 2,221 subjects experienced 111 fatal heart attacks. The placebo group of 2,223 individuals experienced 189 such incidents.

(A) Arrange the data to form a 2-by-2 cross-tabulation of data.

(B) Calculate the RR.

(C) In relative terms, how much did the Zocor decrease the risk of a heart attack?
[Hint: The baseline RR is 1, indicating no difference in risk. The increase or decrease in risk terms is equal to the RR – 1, with negative values representing a relative decrease and positive values represent relative increases. We then convert the proportion to a percentage and say “There was a xx% [increase or decrease] in risk in relative terms,” or something  like that.]

8.10 Cell phone use and auto accidents. One aspect of cell phone use that deserves our attention is its potential to cause driving accidents. Dreyer (1999) estimated fatal auto accidents rates of 5, 10, and 12 per 100,000 person-years for light, moderate, and heavy cell phones use. Using the light users as the reference category, calculate the effect of moderate- and heavy-use in absolute terms. 

8.11 Strong associations do not necessarily affect large numbers of people. Review the data in Table 8.6 (p. 165) in the text and explain in plain terms why the absolute effect of smoking on ischemic (coronary) heart disease is larger than the effect of smoking on lung cancer occurrence even though smoking is associated with a modest relative risk for heart disease and a large relative risk for lung cancer.

8.12 In plain English. How would you explain each of these epidemiologic measures to a lay audience? (A) risk (B) relative risk (C) risk difference (D) attributable fraction in the population

8.13 Injuries in farm worker [similar to exercise 11.4]. McGwin et al. (2000) completed a cohort study in which farmers were contacted biannually to determine whether an agriculture-related injury had occurred. Results by ownership status and race were as follows:

Group (number)

Events

Person-years

Caucasian Owners (0)

67

2047

Af-Am. Owners (1)

27

821

Af-Am. Workers  (2)

37

359

 

(A) Calculate event rates per 1000 person-years within each group.

(B) Calculate RRs using “group 0” as the reference group.

(C) Is there an association between race and risk?

(D) Is there an association between farm ownership and risk? 

 

8.14 Vitamins and neural tube defects, population preventable fraction. 

 

(A) Take the data from exercise 8.1 and put in into a 2-by-2 table.

(B) Assume data represent a random sample of population pregnancies. Determine the proportion of neural tube defects in the population that would be prevented with universal prenatal folic acid use. [Use formula 8.17 or formula 8.18.]

 

8.15 CMV and restenosis, attributable fraction. 

 

(A) Put the data from exercise 8.3 into 2-by-2 table format.

(B) Calculate the fraction of restenoses in CMV+ patients attributable to this infection (i.e., AFe).

(C) Assume data are a random sample of patients undergoing angioplasty. What fraction of the restenoses in this patient population are attributable to CMV (i.e., AFp)? 

 

8.16. Why is it imprudent to say that a risk ratio of 10 indicates a high risk of disease?