Practice Problems--Midterm

Transcription

1 Practice Problems--Midterm The following problems are similar to those that will appear on your midterm examination. The answers to the problems are given at the end of this lesson Use the following information for questions 1 and 2. An outbreak of gastritis occurred on a cruise ship. The following data were obtained from a questionnaire completed by everybody on board the ship shortly after the outbreak: Persons who ate food Persons who did not eat food Food Sick Well Sick Well Herring Chicken Spinach soufflé Oysters Chocolate mousse What is the most likely infective food on the cruise ship? a. Herring. b. Chicken. c. Spinach soufflé. d. Oysters. e. Chocolate mousse. 2. What is an estimate of the relative risk of developing gastritis associated with herring consumption? a. 0.5 b. 2.0 c. 2.3 d. 8.0 e. It cannot be computed from the data given.

2 3. California Highway Patrol statistics revealed that more accidents involve blue cars than cars of any other color. The inference that while driving a blue car one is at higher risk of an accident than while driving a car of another color is a. correct. b. incorrect, because the comparison is not based on rates. c. incorrect, because no control or comparison group is used. d. incorrect, because no test of statistical significance has been made. e. incorrect, because prevalence is used instead of incidence. 4. In 1945, 1,000 women were identified who worked in a factory painting radium dials on watches. The incidence of bone cancer in these women up through 1975 was compared to that of 2,000 women who worked as telephone operators in 1945 (assume all 3,000 women were followed for the entire 30 years and that the two groups were identical in all respects except for their occupation). Twenty of the radium dial workers and four of the telephone operators developed bone cancer between 1945 and An estimate of the relative risk of developing bone cancer for radium dial workers is a. 2. b. 4. c. 5. d When a new treatment is developed that reduces case fatality for a particular disease, but does not produce recovery from that disease, which of the following will probably occur? a. Prevalence of the disease will decrease. b. Incidence of the disease will increase. c. Prevalence of the disease will increase. d. Incidence of the disease will decrease. e. Incidence and prevalence of the disease will decrease.

3 Use the following information for questions Regionville is a community of 100,000 persons. During 1990, there were 1,000 deaths from all causes. All clinically diagnosed cases of tuberculosis during 1990 have been found, and they total 300, of which 200 were males and 100 were females. During 1990, there were 60 deaths from tuberculosis, 50 of them in males. 6. Crude mortality rate in Regionville in 1990 was a. 300 per 100,000. b. 60 per 100,000. c. 10 per 1,000. d. 100 per 1, The proportionate mortality in 1990 due to tuberculosis is a. 20 percent. b. 30 percent. c. 6 percent. d. 3 percent. 8. An estimate of the tuberculosis case fatality in 1990 would be a. 6 percent. b. 20 percent. c. 2 percent. d. equal in males and females. e. higher in females than in males. 9. The mortality rate in 1990 due to tuberculosis was a. 60 per 100,000 per year. b. 300 per 100,000 per year. c. 200 per 1,000 per year. d. 20 percent. 10. The mortality rate in 1990 due to tuberculosis in males was

4 a. 0.5 per 1,000 per year. b. 25 percent. c. greater in males than in females. d. 50 per 300 per year. 11. Communities P and Q have equal age-adjusted all-cause mortality rates. Community P has a lower crude mortality rate than Q. The best conclusion is that a. the two communities have identical age distributions. b. diagnosis is more accurate in P than Q. c. P has an older population than Q. d. Diagnosis is less accurate in Q than P. e. P has a younger population than Q. 12. In three large series of cases of disease, the gender distribution was found to be as follows: Series Male cases Female cases Total The incidence rate of this disease, by gender, was a. twice as great in males as in females. b. three time greater in males than in females. c. five times greater in males than in females. d. from two to five times as great in males as in females.

5 Use the following information to answer questions A large study of bladder cancer and cigarette smoking in Boston produced the following data: Bladder cancer incidence rates per 100,000 males Cigarette smokers 48.0 Nonsmokers The relative risk of developing bladder cancer for male cigarette smokers compared with male non-smokers is a b per 100,000 male smokers per year. c d percent. 14. Assume that cigarette smoking is a cause of bladder cancer. The attributable risk of bladder cancer due to cigarette smoking in male cigarette smokers is a b per 100,000 male smokers per year. c d per 100,000 male smokers per year. 15. Assume that cigarette smoking is a cause of bladder cancer. The population attributable risk percent for bladder cancer due to smoking in males in Boston is a b per 100,000 per year. c d percent. 16. Assume that cigarette smoking is a cause of bladder cancer, and that during the time that this study was conducted 300 cases of bladder cancer were diagnosed among male smokers in Boston. About how many of these cases occurred because these men were smokers?

6 a b per 100,000 per year. c d e. It cannot be computed from the data given. 17. A community-wide x-ray survey was conducted in a rural county in the first week of June 1945 in order to identify persons with active tuberculosis. Race Population surveyed Active cases found Active cases per 1,000 White 22, Black 15, The results of this survey were interpreted as contradicting the widely held view that blacks are more prone to develop active tuberculosis than whites. This interpretation is a. justified given the data. b. not justified given the data. 18. In 1960, the blood pressure of a group of 500 men aged 21 to 24 was examined. The same men were re-examined every five years for the next 30 years. The results are shown in the following table: Year of examination Age at time of each examination Number of men Mean diastolic blood pressure Choose the one best answer: these data show that in this sample of men, a. diastolic blood pressure rose in all men with increasing age. b. no statement concerning the relationship of age to blood pressure can be made from these data because the cohort effect is not known. c. no statement concerning the relationship of age to blood pressure can be made from these data because the effect of selective survival is unknown. d. none of the above statements is correct.

7 19. Approximately 11.4% of the deaths in children aged 1 14 years in the United States in 1989 were due to cancer. Approximately one-quarter of the deaths among persons 65 years of age or older were due to cancer in that year. Is it correct to say that these data indicate that the risk of death from cancer was approximately twice as great in the older age group than the younger age group? a. Yes. b. No. 20. Most cancer incidence statistics for the United States come from areas with population-based cancer registries. Age-specific incidence rates are computed by enumerating the number of new cases in a given age group during a certain time period, and dividing by the estimated mid-time period population in that age group. From 1960 to 1975, the annual number of hysterectomies performed on American women increased much faster than the size of the female population aged 15 and over. Virtually all of the increase was accounted for by hysterectomies done for nonmalignant indications. What effect would you predict this trend would have on the observed case fatality for uterine cancer? a. The case fatality would be too high. b. The case fatality would be too low. c. The case fatality would not change. d. It depends on the difference in treatments among women with hysterectomies and without hysterectomies. e. None of the above. 21. Suppose that the incidence rate of a particular disease is the same in every county in Washington State, and that the frequency of a particular exposure (suspected as a possible risk factor for the disease) is also the same in every county in Washington State. Would you be willing to conclude from these data that exposed persons have the same risk of disease as do unexposed persons? Why or why not? (Use no more than two brief sentences for your response.)

8 22. Use the following data to answer parts a, b, and c of this question. Age-adjusted mortality rates per 1,000 per year Disease Nonsmokers Smokers Total population Oral cancer Bladder cancer Stroke Accidents All causes Assuming that smoking is a cause of death due to stroke, oral cancer, and bladder cancer, answer the following questions: a. What is the rate of fatal stroke in the total population that is attributable to smoking? b. What is the rate of fatal oral cancer in smokers relative to nonsmokers? c. What percentage of deaths due to bladder cancer would be prevented if no one in this population had smoked cigarettes? 23. In 1987, Feldman et al. studied the descriptive epidemiology of cancer in the state of Connecticut (MMWR 36:205 7, 1987). They used data from the Connecticut Tumor Registry, a population-based surveillance system that since 1935 has (1) identified all new cancer diagnoses in Connecticut residents, and (2) followed them to evaluate prognosis. The authors estimated various measures of frequency of all cancers combined. The following table is based on their report. Gender Measure Males Females Incidence Prevalence 2 1,789 2,222 Mortality age-adjusted rate per 100,000 per year (for ) 2 age-adjusted per 100,000 on January 1, 1982 One or more of these aspects could be explained a. by a greater prevalence of cancer risk factors among males compared to females, and a tendency for females to develop cancers that are more lethal than those developed by males. b. by a tendency for females to develop cancers that are less lethal than those that males develop. c. only by looking at age-specific data. d. by the ecologic fallacy. e. by none of the above.

9 Questions 24 and 25 concern the following information from a recent report from the CDC (MMWR 41:225 28, 1992): In October 1991, a woman reported that her son and at least 10 other persons who had recently participated in a high school biology field trip to a seaside state park had developed pruritic dermatitis ( swimmer s itch ). The state epidemiologist conducted an investigation of 37 persons who had contact with the sea water during the trip, of whom 30 met the case definition for the outbreak. Among her findings were that (1) cases occurred among 5 of 11 persons who had worn long pants in the water, as opposed to 25 of 26 persons who had worn shorts in the water, and (2) cases occurred among 16 of 19 persons who reported promptly drying the exposed skin with a towel, compared with 14 of 18 who did not promptly dry skin with a towel. 24. An estimate of the relative risk of developing swimmer s itch associated with wearing long pants as opposed to short pants in this outbreak would be a b c d e Based on the data, reasonable advice that the state epidemiologist could have given to the park officials would be to recommend that waders a. dry off promptly after going in the water. b. wear long pants (or similar protective clothing). c. dry off promptly only if one has worn shorts in the water. d. wear short pants. Questions 26 and 27 are based on the following summary of a recent report from the CDC: A recent report examined the epidemiology of traumatic injuries from helicopter crashes during logging operations in Alaska (MMWR 43:472 75, 1994). Between (and including) July 1991 and December 1992, there were 50 helicopter pilots and 25 helicopters involved in logging operations. During this time period, 6 helicopters crashed during logging operations; these crashes resulted in 4 pilot deaths. 26. The crash rate per 100 helicopter-months was a. 6.0.

10 b c d e. 16 percent. 27. The mortality rate for helicopter pilots per 100,000 pilot-years was a. 5,333. b. 10,666. c d. 8,000. e Down s syndrome is one of the most serious and frequently reported birth defects among live-born infants and is an important cause of mental retardation. It is well-established that the prevalence of Down s syndrome at birth increases with increasing maternal age, but few other risk factors have been identified. Investigators at the Centers for Disease Control and Prevention recently examined geographic patterns of Down s syndrome in the United States in an attempt to generate clues to the etiology of this disease (MMWR 43:617 22, 1994). The data were derived from population-based surveillance systems in eight states during (inclusive). Down s syndrome at birth, by state, State Number of cases Number of live births New Jersey ,387 New York 2,121 2,157,413 Illinois ,896 Kansas ,696 Georgia ,332 Maryland ,704 Colorado ,172 Washington ,808 The patterns in the prevalence of Down s syndrome at birth based on these data would be consistent with which one of the following statements? a. The prevalence in Colorado is high because it has the fewest number of cases among the states studies. b. The prevalence in Kansas is particularly low because births are ascertained less completely in that state compared to the others under study.

11 c. The difference between the prevalences in Kansas and Colorado could be due, at least in part, to greater underreporting of Down s syndrome in Colorado compared to Kansas. d. The variation among the eight states could be due to differences in the age distribution of the mothers giving birth in the different populations during the study period. e. The variation among the eight states could not be due to differences in the age distribution of the mothers giving birth in the different populations during the study period. 29. Investigators at the Centers for Disease Control and Prevention recently examined time trends in the occurrence of low birthweight (LBW) infants (MMWR 43:335 39, 1994). The data were derived from birth certificates for live-born U.S. infants during LBW infants were categorized according to whether or not they were term gestations or pre-term gestations, and trends by year were examined. (See the following graph.) Incidence of low birthweight, by gestation and year of birth Term Pre-term Total Year of Birth Conclusions that would be consistent with the one or more aspects of this analysis include all of the following except a. the incidence of LBW infants increased during largely as a result of increases in the incidence of LBW pre-term. b. the trends could be due to the increasing presence, in the U.S. population of pregnant women, of risk factors for pre-termassociated LBW during the study period. c. the incidence of LBW probably increased during because the number of births increased during that time period. d. risk factors for term LBW probably did not increase in the U.S. population of pregnant women during the study period. e. the majority of the increase in the incidence of pre-term LBW appears to have occurred since about

12 Answers to the Practice Midterm Problems 1. b 2. b 3. b 4. d 5. c 6. c 7. c 8. b 9. a 10. e 11. e 12. e 13. c 14. b 15. e 16. d 17. b 18. d 19. b 20. c 21. No such a conclusion would be based on the ecologic fallacy 22. (a) 0.6 per 1,000 per year; (b) 2.0; (c) 10.8% 23. b 24. a 25. b 26. b 27. a 28. d 29. c

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