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Name: _______________________________________________________________________________
Homework #6: Study Design II: Observational Studies
Due Tuesday, November 26th by the End of the Day (11:59 p.m.)
43 Total Points (7% of Grade)
This is an individual homework assignment. While you are allowed to use any notes, textbooks or
readings, and to consult with the faculty instructor, if having trouble, you are expected to think
through this assignment and do it on your own without the collaboration of classmates. You
should wait until after you have listened to Lectures #13, 14, 15 and 16, and read pages 153-158 of
the textbook before starting this homework assignment. Remember to have your notes in front of
you while doing this homework.
Absolutely no late homework assignments will be accepted. Please type your answers,
numbering all of the questions.
Part 1: Neural Tube Defects and Multivitamins (11 points in total)
In 1988 Joseph Mulinare and his fellow investigators reported their findings concerning the
association of neural tube defects (type of birth defects) and periconceptional use of
multivitamins (taking multivitamins around the time they became pregnant) (JAMA 1988; 260:
3141-3145). They selected several groups of infants. One group consisted of “all live-born or
stillborn infants with a diagnosis of anecephaly or spina bifida (the two major kinds of neural
tube defects) born during the years 1968 through 1980 who were registered in the Metropolitan
Atlanta Congenital Defects Program.” The second group consisted of “live-born babies without
birth defects who were randomly chosen from all live births that occurred in the metropolitan
Atlanta surveillance area.” Data on multivitamin use was then obtained. Multivitamin use was
defined as “multivitamin or prenatal vitamin consumption during every month of the entire six
month period …from three months before conception through the third month of pregnancy by
the mother.” The following table presents partial results from that report. (A number of changes
and adjustments have been made to simplify the table for purposes of this example.)
2 by 2 Table for Maternal Multivitamin Use and Neural Tube Defects
Mother took
multivitamins
Mother did not take
multivitamins
Total
Infant born with
Neural Tube Defect
24
Infant not born with
birth defect
411
Total
159
1092
1251
183
1503
1686
435
1) What is the exposure in this study? (1 point)
2) What is the disease outcome in this study? (1 point)
1
Name: _______________________________________________________________________________
3) According to the description above, what were the two comparison groups? (2 points)
4) Were the two comparison groups those with and without the outcome or those with and
without the exposure? (1 point)
5) What type of study design is this? (Choose either case-control or cohort.) (1 point)
6) If this is a cohort study, calculate a relative risk. If it is a case-control study, calculate an
odds ratio. Calculate only the one that goes with this study design, and state which one it
is. Show all steps, including the formula, numerator and denominator. Round off the
final answer to two places after the decimal. (3 points)
7) Is taking multivitamins around the time of conception a possible protective or risk factor
for having a child with neural tube defects? (1 point)
8) Is taking multivitamins strongly associated with neural tube defects (i.e. a strong risk
factor or a strong protective factor) or is it just weakly associated? (Hint: consider a
strong risk factor as being an odds ratio or relative risk > 2.00, and a strong protective
factor as an odds ratio or relative risk < 0.5.) (1 point) Part 2: Maternal Drug Consumption and Birth Defects (12 points in total) As an epidemiologist you are going to investigate the effect of a drug suspected of causing malformations in newborn infants when the drug in question is taken by pregnant women during the course of their pregnancies. As your sample, you will use the next 250 single births occurring in a given hospital. You will follow these mothers during the entire course of their pregnancies, maintaining a complete and accurate record of drug use during pregnancy. This will be achieved not only through interviewing the women, but in addition, you will review medical records to verify use of the drug. At the end of the study, the resultant data turn out to be: Fifty mothers have taken the suspected drug during their pregnancies. Of these mothers, 42 have delivered malformed infants. In addition, there are 15 other infants born with malfunctions to women who have not taken the drug. 1) 2) 3) 4) 5) What is the exposure in this study? (1 point) What is the disease outcome in this study? (1 point) What type of study design is this? (Choose either case-control or cohort.) (1 point) Explain how you know that it is this study design. (2 points) Construct a two by two table with all labeled columns and rows, including totals for this study. (2 points) 6) If this is a cohort study, calculate a relative risk. If it is a case-control study, calculate an odds ratio. Calculate only the one that goes with this study design, and state which one it is. Show all steps, including the formula, numerator and denominator. Round off the final answer to two places after the decimal. (3 points) 7) Is the exposure possible protective or risk factor for the outcome? (1 point) 8) Is the exposure strongly associated with the outcome (i.e. a strong risk factor or a strong protective factor) or is it just weakly associated? (Hint: consider a strong risk 2 Name: _______________________________________________________________________________ factor as being an odds ratio or relative risk > 2.00, and a strong protective factor as
an odds ratio or relative risk < 0.5.) (1 point) Part 3: Study Design Identification (20 points in total, 2 points each) For each of the descriptions below, identify the study design. Choose only one study design per description: ecologic, cross-sectional, case-control, or cohort study. Write the type of study design that applies below each description. Example: A) The level of unemployment was used as a measure of economic distress in Germany. Researchers examined the association between economic distress and general anxiety syndrome across states in Germany. Study Design: Ecologic 1. Young women who had suffered a stroke were compared with those who had not had a stroke on their use of oral contraceptives. Study Design: 2. A study was designed to find out if high rates of tuberculosis were associated with high rates of AIDS in a population. The rates of tuberculosis in 50 countries was correlated with the rates of AIDS in those same countries. Study Design: 3. Parents of 863 one-month old Australian children were interviewed about the infant’s sleeping environment. When these families were interviewed again 7 years later, it was found that those infants who had used synthetic bedding items at one month of age were more likely to develop asthma by the time they were seven years old than those whose bedding items were completely made of natural materials. Study Design: 4. A survey was conducted to discover the prevalence of overweight among Texas schoolchildren. Study Design: 3 Name: _______________________________________________________________________________ 5. The entire population of a given community is examined and all who are judged free of bowel cancer are questioned extensively about their diet. These people are then followed for several years to see whether their eating habits will predict their risk of developing bowel cancer. Study Design: 6. An investigator collects information on the size of factories and their rates of accidents. She finds that the five largest factories have accident rates that are 50% higher than the five smallest factories. Study Design: 7. A random sample of 300 people over the age of 65 with Parkinson’s Disease was obtained through the National Parkinson’s Foundation. These were compared with 300 people over age 65 who were randomly sampled from Medicare files, and had no diagnosis of Parkinson’s Disease, on a variety of lifestyle factors. Study Design: 8. The prevalence of genital infection with chlamydia trachomatis among women of childbearing age was ascertained in a survey conducted in Houston. Study Design: 9. Two hundred babies were followed from birth to age five to determine if those whose mothers smoked during pregnancy were more likely to have respiratory infections in the first five years of life than those whose mothers did not smoke during pregnancy. The findings supported the investigators’ assumption that smoking during pregnancy increases the frequency of respiratory infections in young children. Study Design: 10. Fifty patients recently diagnosed with hepatitis A were selected along with another 50 patients without hepatitis A from among those attending a local clinic. The participants in the two groups were then interviewed to determine if they had any body piercing within the last two months. Study Design: 4 COHORT STUDIES Lecture 16 Cohors = Latin: Warriors, 1/10 of a Roman Legion ◦ The term cohort is said to originate from the Latin cohors, which referred to one of ten divisions of an ancient Roman legion, part of the Roman army. Epidemiologist’s Definition: ◦ A designated group of persons who are followed or traced over a period of time Cohort Studies: Longitudinal Studies with Data on Individuals Epidemiology Observational Individuals Groups Ecologic Experimental CrossSectional CaseControl Cohort Groups Individuals Community Interventions Clinical Trials ◦ An analytic study attempts to identify causes or risk factors that explain healthrelated states or events. Cohort Studies are Analytic ◦ It tests specific a priori (previously formed) hypotheses often developed in descriptive studies. ◦ Has a Comparison group. ◦ Examines associations between exposure(s) and outcome(s) ◦ It begins with people with the exposure and compares them to people without the exposure (comparison group) over time in respect to incidence (or mortality) of the disease. Chief Characteristic of a Cohort Study Design of a Cohort Study Disease Exposed Source Population People without the disease: Sample of the Population at Risk Not Exposed No Disease Disease No Disease Start with the Population at Risk Population of interest should be reviewed to ascertain those people or groups that are susceptible to becoming cases. Individuals who already have a disease outcome of interest (prevalent cases) or who are not at risk (e.g., they have had an organ removed such that they cannot become a case) should be excluded from the study. Cohort Studies: Characteristics ◦ Start with a group of participants who lack a positive history of the outcome of interest and are at risk for the outcome. ◦ Include at least two observation points: 1. one to determine eligibility and exposure status 2. a second (or more) to determine the number of incident cases. ◦ The same individuals are followed over time. Example 1 of Cohort Study The Alameda County Study • Involved residents of Alameda County, CA, ages 16-94 years. • Data collected through mailed questionnaires; telephone interviews or home interviews of non-respondents. • Began in 1965. • Follow-up in ◦ ◦ ◦ ◦ ◦ 1973, 1985, 1988, 1994, and 1999. Source of Map: https://upload.wikimedia.org/wikipedia/commo ns/4/4c/California_map_showing_Alameda_Co unty.png “ The Alameda 7” Studied lifestyle factors associated with health and mortality. 1. Having Never Smoked 2. Drinking Less Than 5 Drinks at One Sitting 3. Sleeping 7- 8 Hours a Night 4. Exercising 5. Maintaining Desirable Weight for Height (Normal BMI) 6. Avoiding Snacks 7. Eating Breakfast Regularly Example 2 of a Cohort Study: Framingham Heart Study ◦ Conducted in Framingham, Massachusetts. ◦ Used a random sample of 5,209 from targeted age range of 30 to 62 years in 1948. ◦ Longest Ongoing study of Coronary Heart Disease in the world ◦ In the 3rd Generation of Participants. ◦ http://www.framinghamheartstudy.org/ Source of Map: https://upload.wikimedia.org/wikipedia/comm ons/3/3f/Framingham_ma_highlight.png Source of Logo: https://upload.wikimedia.org/wikipedia/commons/thumb/0 /03/US-NIH-NHLBI-OldLogo.svg/602px-US-NIH-NHLBIOldLogo.svg.png Framingham Study (Film) ◦ Study of heart disease and stroke risk factors. ◦ Ongoing study of Coronary Heart Disease initiated in 1948. ◦ Later recruited children and grandchildren of original participants ◦ Examine participants every two years Some Research Milestones from the Framingham Heart Study ◦ 1960: Cigarette smoking found to increase risk of heart disease. ◦ 1961: Cholesterol level, blood pressure, and electrocardiogram abnormalities found to increase risk of heart disease. ◦ 1967: Physical activity found to reduce risk of heart disease and obesity to increase risk of heart disease. ◦ 1970: High blood pressure found to increase risk of stroke. ◦ 1976: Menopause found to increase risk of heart disease. ◦ 1978: Psychosocial factors found to affect heart disease. ◦ 1978: High levels of HDL cholesterol found to reduce risk of death. ◦ 1999: Lifetime risk at age 40 of developing coronary heart disease is 50% for men and 33.3% for women ◦ 2002: Lifetime risk of developing high blood pressure in middle-aged adults is 90% https://www.framinghamheartstudy.org/fhs-about/research-milestones/ Begun in 1995, the first questionnaire was mailed to subscribers to Essence magazine and members of several professional organizations. 59,000 women who completed and returned that questionnaire are being followed. To study many illnesses, such as hypertension, breast cancer, stroke, and lupus in black women. https://www.bu.edu/bwhs/ Example 3: The Black Women’s Health Study (BWHS) Example #4: The Nurses’ Health Study I, II and III ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ Nurse’s Health Study I: Began in 1976 with 121,700 nurses Originally studied oral contraceptive use; expanded to women’s health. Married female R.N.s ages 30-55 years. Data collected through mailed questionnaires. Follow-up every 2 years; toenail sample at year 6 and blood sample at year 13. Nurses’ Health Study II: started in 1989 with 116,430 female nurses between 25 and 42 years old Nurses’ Health Study III: both male and female nurses, web-based, started in 2010, still recruiting http://www.channing.harvard.edu/nhs/ • A study in which a group of people is followed over time. • The group is made up of people who have the exposure of interest and people who do not have the exposure of interest. Cohort Study • Exposed and unexposed people are followed over time to determine whether they experience the outcome. Chief Characteristic of a Cohort Study ◦It begins with people with the exposure and compares them to people without the exposure (comparison group) over time in respect to incidence of the disease. HOW IS THE DESIGN OF A COHORT STUDY DIFFERENT THAN THE DESIGN OF A CASE-CONTROL STUDY? Design of Case Control Study: Retrospective Time Direction of inquiry: backwards Exposed Not exposed Exposed Not exposed Cases (diseased) Population Controls (disease free) Design of a Cohort Study Direction of Inquiry: Forward in Time Disease Exposed No Disease Population People without the disease Disease Not Exposed Time Direction of inquiry: forward No Disease Comparison of Case-Control and Cohort Studies Case-Control Study ◦ Comparison Groups: Those with and without the outcome ◦ Data collected from the cases (with the outcome) and the controls (without the outcome) at one point in time. ◦ They may be asked about the past, but are not followed over time. ◦ The disease (or other outcome) has already occurred when the study begins. Cohort Study ◦ Comparison Groups: Those with and without the exposure ◦ Data collected from the exposed and not exposed (entire cohort) at several points in time. ◦ They are followed over time to see what happens to them. ◦ The disease (or other outcome) has not occurred when the study begins. Cohort Studies permit calculation of incidence (and mortality) rates. ◦ Can be thought of as going from cause to effect. Earlier Exposure Later Disease or Death Incidence ◦ Rate of development of disease during a given period of time ◦ Three key elements: ◦ Only new cases included in numerator ◦ Total population at risk in the denominator ◦ Time element – period over which new cases developed Cohort Studies: Measures of Association Relative risk provides a direct measure of association between exposure and outcome. Relative risk is the ratio of the incidence of disease in the exposed group to the incidence in the non-exposed group. Risk ◦ The probability that an event will occur, for example, that an individual will become ill or die, within a specified period of time Relative Risk ◦ A way of quantifying the relationship between two risks ◦ Tells us the number of times one risk is larger or smaller than another Ratio ◦ A fraction with no specified relationship between numerator and denominator ◦ Range: 0 to  ◦ A/B ◦ Examples ◦ Prevalence Ratio (ratio of prevalence proportions) ◦ Odds Ratio (ratio of two sets of odds) ◦ Relative Risk (ratio of two incidences) Relative Risk Relative risk = Incidence rate in the exposed Incidence rate in the non-exposed ◦ Research Question: Is there an association between child abuse and suicide attempts among chemically dependent adolescents? ◦ Source: Deykin EY, Buka SL. Am J Public Health. 1994;84:634-639. Cohort Studies: Relative Risks Sample Calculation Numerator and Denominator Numerator Denominator Incidence of the Outcome Among Exposed Incidence of the Outcome Among unexposed Incidence (Ie) = a / (a+b) Incidence (Io) = c / (c+d) With Without Outcome Outcome Total Exposed A B A+B Not Exposed C D C+D Total A+C B+D N (A+B+C+D) Relative Risk is calculated like the Prevalence Ratio, but has a different meaning. ◦ Relative Risk = [A/(A+B)] / [C/(C+D)] Suicide Attempt and History of Sexual Abuse among Male Chemically Dependent Adolescents History of Suicide Attempt Sexual Abuse No Suicide Totals Attempt Yes A = 14 B=9 A + B = 23 No C = 49 D = 149 C + D = 198 Total A+C = 63 B+D = 158 N = 221 Relative Risk = (14/23) / (49/198) = 0.6087 / 0.2475 History of Suicide Attempt Sexual Abuse No Suicide Totals Attempt Yes A = 14 B=9 A + B = 23 No C = 49 D = 149 C + D = 198 Total A+C = 63 B+D = 158 N = 221 = 2.46 Is the Exposure Protective or a Risk Factor? Positive Association Negative or Inverse Association Protective 0 No Association 1 Risk Factor  How to Interpret Relative Risks Positive Association Negative or Inverse Association Possibly Protective Exposure Possible Risk Factor No Association 1  0 Stronger Weaker 2.46 Stronger How to tell from the Relative Risk if the exposure may be protective or a risk factor ◦ RR=1 implies no association. ◦ Assuming statistical significance ◦ (which you only know from a p-value): ◦ RR >1 suggests the exposure is a risk factor for the outcome
◦ RR<1 suggests a protective factor ◦ The further away from one (smaller or larger) that the RR is, the stronger the association is. Calculated like a Prevalence Ratio, but… ◦ It is two incidence rates (or risks) that you are comparing – not two prevalence proportions ◦ Since incidence is ONLY influenced by the exposure – not by duration of disease ◦ A relative risk is a stronger measure of a possible causal relationship. Advantages of Cohort Studies ◦ Permit direct determination of incidence (risk) ◦ Time sequencing of expos ... Purchase answer to see full attachment

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