Advantage of a prospective cohort study.

“Please answer all the questions and provide rationale for the answer for each question using your own wordsand show your calculations to get full credit”.

1. Which of the following is a case-control study? [ONE POINT]
2. Study of past mortality or morbidity trends to permit estimates of the occurrence of disease in the future

1. Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under studyc. Analysis of previous research in different places and under different circumstances to permit the establishment of hypotheses based on cumulative knowledge of all known factors
2. Study of the incidence of cancer in men who have quit smoking
3. Both a and c

1. In a study of a disease in which all cases that developed were ascertained, if the relative risk for the association between a factor and the disease is equal to or less than 1.0, then: [ONE POINT]

1. There is no association between the factor and the disease
2. There is either no association or a negative association between the factor and the disease
3. The factor protects against development of the disease
4. Either matching or randomization has been unsuccessful
5. The comparison group used was unsuitable, and a valid comparison is not possible

1. A random sample of middle age sedentary males was selected from four census tracts, and each man was examined for coronary artery disease. All those having the disease were excluded from the study. All others were randomly assigned to either an exercise group, which followed for a two-year program of systematic exercise, or to a control group, which had no exercise program. Both groups were observed semiannually for any difference in incidence of coronary heart disease.

• What type of study (study design) you would assign to this information? Why? [ONE POINT] 

4.       Several studies have found that approximately 95% of cases of lung cancer are due to cigarette smoking. This measure is an example of: [ONE POINT]a. An incidence rate b. A relative risk c. A prevalence risk d. A proportionate mortality ratioe. An attributable risk

Questions 5 and 6 refer to the following information:

	OUTCOME AFTER 10 YRS
At Beginning of Study	CHD Developed	CHD Did Not Develop
2,000 Healthy smokers	100	1,900
4,000 Healthy nonsmokers	30	3,970

The results of a 10-year cohort study of smoking and coronary heart disease (CHD) are shown above: 5.      The incidence of CHD in smokers that can be attributed to smoking is: [ONE POINT]6.       The proportion of the total incidence of CHD in smokers that is attributable to smoking is: [ONE POINT]

1. What type of study design is considered to be the ‘gold standard’ in assessing causality? [ONE POINT]

1. Cohort
2. Case-control
3. Ecological
4. Experimental

1. All of the following are important criteria when making causal inferences except: [ONE POINT]

1. Consistency with existing knowledge
2. Dose-response relationship
3. Predictive value
4. Consistency of association in several studies
5. Strength of association
6. All of the following are measures of process of health care in a clinic except: [ONE POINT]
   1. Proportion of patients in whom blood pressure is measured
   2. Proportion of patients advised to stop smoking
   3. Proportion of patients whose height and weight are measured
   4. Proportion of patients who have complications of a disease
   5. Proportion of patients whose bill is reduced because of financial need

1. Colon cancer is diagnosed in 45 patients per year within a community of 10,000 unaffected individuals. A screening test is applied to all residents of this community.

• What is the sensitivity (in %) of the screening test, if it detects 38 of the colon cancer patients. What is the specificity if the test correctly determines that 9,750 of the unaffected persons who do not have colon cancer? What is the positive predictive value? What is the negative predictive value

[Interpret the results and show your calculations for full credit].

1. The sensitivity of the test is [ONE POINT]_____________
2. The specificity of the test is [ONE POINT] ______
3. The positive predictive value of the test is [ONE POINT] _____________
4. The negative predictive value of the test is [ONE POINT] ____________
5. What are your overall comments about the validity of this test? [ONE POINT]

1. Which of the following is not an advantage of a prospective cohort study? [ONE POINT]

1. Precise measurement of exposure is possible
   b. Incidence rates can be calculated
2. It usually costs less than a case-control study
   d. Recall bias is minimized compared with a case-control study
   e. Many disease outcomes can be studied simultaneously
3. A major problem resulting from the lack of randomization in a cohort study is: [ONE POINT]
4. The possibility that a greater proportion of people in the study may have been exposed
   b. The possibility that a smaller proportion of people in the study may have been exposed
5. The possibility that a factor that led to the exposure, rather than the exposure itself, might have caused the disease
   d. That, without randomization, the study may take longer to carry out
   e. Planned crossover is more likely

1. Which of the following is an approach to handling confounding? [ONE POINT]
   1. Individual matching
   2. Stratification
   3. Group matching
   4. Adjustment
   5. All of the above

1. It has been suggested that physicians may examine women who use oral contraceptives more often or more thoroughly than women who do not. If so, and if an association is observed between phlebitis and oral contraceptive use, the association may be due to: [ONE POINT]

1. Selection bias
   b. Interviewer bias
   c. Nonresponse bias
   d. Recall bias
   e. Surveillance bias
2. Residents of three villages with three different types of water supply were asked to participate in a survey to identify cholera carriers. Because several cholera deaths had occurred recently, virtually everyone present at the time underwent examination. The proportion of residents in each village who were carriers was computed and compared. What is the proper classification for this study? [ONE POINT]
3. Case-control study
   b. Concurrent cohort study
   c. Non-concurrent cohort study
4. Cross-sectional study
   e. Experimental study

Question 16 is based on the information given below:

In a case-control study of the relationship of radiation exposure and thyroid cancer, 50 cases admitted for thyroid cancer and 100 “controls” admitted during the same period for treatment of hernias were studied.  Only the cases were interviewed, and 20 of the cases were found to have been exposed to x-ray therapy in the past, based on the interviews and medical records.  The controls were not interviewed, but a review of their hospital records when they were admitted for hernia surgery revealed that only 2 controls had been exposed to x-ray therapy in the past.

1. Based on the description given above, what source of bias is least likely to be present in this study? [ONE POINT]

1. Recall bias
2. Bias due to loss of subjects from the control group over time
3. Bias due to controls being non-representative of the non-diseased population
4. Bias due to use of different methods of ascertainment of exposure in cases and controls
5. Selection bias for exposure to x-ray therapy in the past
6. Of 3,000 persons who had received radiation treatment in childhood because of an enlarged thymus, cancer of the thyroid developed in 40 and a benign thyroid tumor developed in 80. A comparison group consisted of 5,000 children who had received no such treatment (brothers and sisters of the children who had received radiation treatment).  During the follow-up period, none of the comparison group developed thyroid cancer, but benign thyroid tumors developed in 10.

Calculate the relative risk for benign thyroid tumors. Using your own words, interpret the relative risk. [ONE POINT]

1. The extent to which a specific health care treatment, service, procedure, program, or other intervention does what it is intended to do when used in a community-dwelling population is termed its: [ONE POINT]
2. Efficacy
   b. Effect modification
   c. Efficiency
3. Effectiveness
   e. None of the above
4. The best index (indices) for concluding that an early detection program for breast cancer truly improves the natural history of disease, 10 years after its initiation, would be: [ONE POINT]

1. A smaller proportionate mortality for breast cancer 10 years after initiation of the early detection program compared to the proportionate mortality prior to its initiation
2. A decrease in incidence of breast cancer
3. A decrease in the prevalence of breast cancer
4. Improved long-term survival rates for breast cancer patients (adjusted for lead time)
5. None of the above

1. In general, screening should be undertaken for diseases with the following feature(s): [ONE POINT]

1. Diseases with a natural history that can be altered by medical intervention
2. Diseases with a low prevalence in identifiable subgroups of the population
3. Diseases for which case-fatality rates are low
4. Diseases that are readily diagnosed and for which treatment efficacy has been shown to be equivocal in evidence from a number of clinical trials
5. None of the above
6. When a new treatment is developed that prevents death but does not produce recovery from disease, the following will occur: (ONE POINT)

1. Prevalence of the disease will decrease
2. Incidence of the disease will increase
3. Incidence of the disease will decrease
4. The incidence and the prevalence of the disease will decrease
5. Prevalence of the disease will increase