University of North Carolina
                            School of Public Health
                          Department of Epidemiology
                    Fundamentals of Epidemiology (EPID 168)
                  Victor J. Schoenbach and Wayne D. Rosamond

                 Fall 1996 Final Exam (Tuesday 10 Dec 1996)

    This examination is based on Per-Gunnar Persson, Anders Ahlbom, Goran
    Hellers.  Diet and inflamatory bowel disease: a case-control study.
    Epidemiology 1992;3:47-52.

    NOTE:  For simplicity, ignore the requirement that this study was
    restricted to those persons with a telephone number.

    1.  Which of the following best describes the primary objective of this
        study? (Choose one best answer) (3 pts)

        A. To test the hypothesis that persons with inflammatory bowel disease
           are more likely to have been exposed to certain dietary factors than
           those without inflammatory bowel disease.

        B. To test the hypothesis that the risk of having inflammatory bowel
           disease given that you have certain dietary exposures is greater than
           the risk of not having inflammatory bowel disease.

        C. To test the hypothesis that the increase in inflammatory bowel
           disease in the population is attributed to certain dietary exposures.

        D. To test the hypothesis that the average consumption of certain
           dietary factors increases as the proportion of a group of people with
           inflammatory bowel disease increases.

    2.  Designation as a case of ulcerative colitis was based on which of the
        following classification models.  (Choose one best answer) (3 pts)

        A. Manifestational criteria

        B. Causal criteria

        C. Both manifestational and causal criteria

        D. Neither 

    3.  Medical records were used to validate the hospital diagnoses of Crohn's
        disease and ulcerative colitis.  By using this validation process
        instead of relying on hospital discharges coding alone, the authors are
        reducing which of the following sources of error?  (Choose one best
        answer) (3 pts)

        A.  Selection bias

        B.  Prevalence-incidence bias

        C.  Information bias

        D.  Surveillance bias
_                                     -2-

    4.  Controls were selected as a random sample using the population register
        of Stockholm County Council.  Which of the following best describes the
        primary purpose of using a random sample in this study?  (Choose one
        best answer) (3 pts)

        A. Maximize generalizability by obtaining a statistically representative

        B. Select a control group that was as similar as possible to the case
           group except for dietary exposures.

        C. Provide an estimate of the dietary exposure in the source population
           from which the cases arose.

        D. Select a control group with dietary habits similar to those in the
           population of cases.

    5.  Dietary exposures were assessed using a questionnaire with
        Òretrospective questions aimed at a period of time 5 years in the pastÓ
        (page 48).  Which of the following situations of misclassification would
        make sucrose appear more harmful than it really was?  (Choose one best
        answer) (3 pts)

        A. Controls underreported sucrose intake but cases did not.

        B. Cases underreported sucrose intake but controls did not.

        C. Both cases and controls underreported sucrose intake.

        D. Both cases and controls overreport sucrose intake.

    6.  Suppose that cases excluded due to administrative delay problems were
        more likely to have daily soft drink exposure than less than daily.
        Which of the following best describes the impact this would have on the
        odds ratio presented in Table 3?  (Choose one best answer) (3 pts)

        A. Without the exclusion the odds ratio would be closer to the null.

        B. Without the exclusion the odds ratio would be larger.

        C. The exclusion did not affect the odds ratio.

        D. Cannot determine on the basis of this information.

    7.  Diagnoses of disease were verified in this study. Define validity and
        compare and contrast this concept with reliability. (4 pts)

    8.  This study uses a case control design with a population based control
        group.  Which of the following, in general, is a strength of this
        design.  (Choose one best answer) (3 pts)

        A. Allows examination of rare diseases.

        B. Allows examination of rare exposures.

        C. Good for establishing temporality.

        D. Good for equalizing on known and unknown confounders.
_                                     -3-

    9.  Items on the food frequency questionnaire were mostly in a format with
        six response options that ranged from twice per day or more often to
        less frequently than once every 2 weeks (pg 48).  In deriving values for
        daily energy intake, the authors treated the food frequency responses as
        which level of measurement?  (Choose one best answer) (3 pts)

        A. Nominal

        B. Ordinal

        C. Interval

        D. Ratio

   10.  Control for age in the analyses presented in Table 2 was accomplished
        through which of the following methods?  (Choose one best answer)
        (3 pts)

        A. Stratified analysis plus matching.

        B. Matching plus mathematical modeling.

        C. Restriction without stratification

        D. Mathematical modeling and stratification.

   11.  Based on the data presented in Table 2, is ulcerative colitis associated
        with fat intake among men?  Give a brief statement to support your
        answer.  (4 pts)  

   12.  The authors state on page 49 that after controlling for smoking, the
        relative risk for CrohnÕs disease among men was 1.9 for a high
        consumption of sucrose and 0.7 for a high consumption of fiber. Briefly
        explain why based on these data the authors state that smoking did not
        confound these associations. (3 pts)

   13.  The data presented in Table 3 indicate that Crohn's disease is
        associated with the consumption of fast foods.  Suppose that when
        stratified by educational attainment, the resulting data were as
                                    Educational attainment

                                  High                    Low

                          Controls   Cases          Controls   Cases

           Fast foods

           1+ times/wk       12        10               8        14

           None             150       100             135        28

        a. Calculate the crude and stratum-specific odds ratios.  (3 pts)

        b. Is this association between fast food and CrohnÕs disease confounded
           by  education level?  Quantify and briefly explain your answer.  (3

        c. Briefly explain in 2 sentences or a diagram how education might fit
           into a conceptual model consisting of fast food, education, and risk
           of Crohn's disease. (3 pts)
_                                     -4-

   14.  In the discussion (page 50), the authors state that Òif the change in
        diet is the same in cases as in controls, then the relative risk
        estimates would be biased toward unityÓ.  This is an example of which of
        the following?  (Choose one best answer) (3 pts)

        A. Non differential misclassification bias
        B. Non differential selection bias
        C. Differential information bias
        D. Differential misclassification bias

   15.  This articles does not present p-values yet reports 95% confidence
        intervals for all odds ratios.  Which of the following best describes
        what information a confidence interval conveys that a p-value does not.
        (Choose one best answer) (3 pts)

        A. A confidence interval puts the observed point estimate in the context
           of randomness.

        B. A confidence interval provides information on the precision of the
           point estimate.

        C. A confidence interval includes an estimate of the statistical power
           of the study.

        D. A confidence interval reflects the clinical significance of the point

   16.  The study describes the association of consumption of Muesli-type
        breakfast cereal and Crohn's disease (Table 3).  Briefly state and
        evaluate the strength of the numerical evidence for the association
        between Muesli-type breakfast cereals and Crohn's disease.  (3 pts)

   17.  Briefly present the evidence for or against the role of fiber as a
        confounder of the association of sucrose intake and CrohnÕs disease.  (3

   18.  Suppose a follow-up to this study was done to estimate the rate (per
        10,000 person years) of ulcerative colitis among a large sample in the
        Swedish population.  The table below summarizes the results.

                                        Fast food intake  

           Soft drink intake            2/week      None

               Daily                     18.0         9.1

               Less frequently            6.8         3.7

        a. Which model for the joint effect of these two food items, the
           additive model or the multiplicative model, better fits the data?
           Your answer should give the formula for each model and show how to
           evaluate it with the above data.  (5 pts) 

        b. Do these data, assuming that they accurately reflect causal effects,
           indicate a synergistic effect from a public health perspective?
           Justify your answer and state an appropriate public health
           implication if any.  (2 pts)
_                                     -5-

   19.  This study did not differentiate between caffeinated and decaffeinated
        coffee.  Using the data presented in Table 4 and applying the
        assumptions below, calculate the odds ratio (heavy versus no use)
        associated with caffeinated coffee consumption and determine if it is
        protective against ulcerative colitis.  Describe in 2 sentences or less
        the interpretation of this new odds ratio, ignoring issues of random
        error. (4 pts)


        1. 20% of the heavy coffee drinkers ( 3 cups per day) among cases drink
           only decaffeinated coffee.

        2. 90% of heavy coffee drinkers among controls drink only decaffeinated

   20.  Which of the following variables was NOT in the multiple logistic model
        that was used to estimate the relative risk for sucrose intake in
        relation to ulcerative colitis in women?  (Choose best answer) (3 pts)

        A. Age

        B. Gender

        C. Total energy intake

        D. Ulcerative colitis

   21.  In the multiple logistic model that yielded the relative risk estimate
        of 0.7 for Ulcerative colitis in relation to daily vegetable consumption
        (Table 4), what was the value of the coefficient for the vegetable
        consumption variable assuming that it was coded as 1=daily, 0=less
        frequently?  Write the conversion equation of coefficient to relative
        risk estimate.  (3 pts)

   22.  Assume that the population of Stockholm County in the age range covered
        by this study was 1,000,000 in 1980 and remained constant throughout the
        decade.  What was the average annual incidence of hospital-diagnosed
        Crohn's disease during that period regardless of when their medical
        record became available?  (3 pts)

   23.  Using the data in Table 2, for which of the following two associations
        is there more of an indication of confounding by age and total energy
        intake in WOMEN?  Support your answer with relevant data and/or
        computations.  (3 pts)

        a. Crohn's disease and sucrose intake (highest versus lowest level)

        b. Crohn's disease and disaccharide intake (highest versus lowest level)

   24.  Briefly state one major strength and one major limitation of this study
        (2 pts)
_                                     -6-

   25.  List two Bradford Hill criteria for evaluating whether dietary sucrose
        intake is causally related to inflammatory bowel disease.  Evaluate each
        using specific facts from the article.  (4 pts)

   26.  Which of the following statements about the data in Tables 1 and 2 are
        TRUE and which are FALSE (answer TRUE or FALSE for each statement).  (2
        pts each)

        a. In women, the rate of (hospitalized) ulcerative colitis was higher
           than that of (hospitalized) Crohn's disease.

        b. The similarity in age distribution between the case groups and
           controls indicates that the rates of these disease are fairly uniform
           between the ages of 15 and 79 years.

        c. Reporting of dietary intake by the Crohn's disease cases involved
           recall over longer periods of time, on the average, than was the case
           for the ulcerative colitis cases.

        d. The proportion of controls with high dietary fat intake was higher
           for men than for women.

   27.  A Swedish friend of yours who lives in Stockhom has an indentical twin
        sister who is anything but identical in terms of her diet.  Your friend,
        as other health conscious Swedes, avoids fast foods and soft drinks, and
        eats whole grain bread and muesli-type cereals daily.  Her twin sister,
        and many Swedes, often consumes fast foods and soft drinks, but never
        touches whole grain bread or muesli.

        Your friend comes to visit with you over the holidays, and while you are
        sleeping late one morning she comes across your class notes from EPID
        168.  At breakfast, where she has been busily scribbling on her napkin,
        she asks you this question.

        "Suppose that fast foods, soft drinks, whole grain bread, and muesli-
        type cereal affect Crohn's disease risk independently, and that I can
        ignore other risk factors.  Suppose also that the excess risks are
        additive.  Is my twin sister's risk of Crohn's disease 10 times my own?"

        She shows you how she used the information in Table 3 to obtain that

        (3.4 - 1) + (2.8 - 1) + ((1/0.4) - 1) + ((1/0.2) - 1) + 1 = 10.7

        She goes on to explain "(3.4 -1) is the excess risk from fast foods, and
        ((1/0.4) - 1) is the excess risk from eating bread that is not whole

        Even though you're not quite fully awake, you feel justifiable pride in
        your command of epidemiologic concepts and explain to her the one big
        mistake she has made.  You say, " . . . ".  Write a brief statement of
        what you would say. (4 pts)

Rosemond/Schoenbach, 12/96, edited 11/11/97  epid168 \ exams 1996 Final exam