#9. You have been asked to investigate an association between being born with lo

Question

#9. You have been asked to investigate an association between being born with lower birth- weight and having elevated blood pressure when older (40-50 years). Choose either a Cohort Study design or a case Control Study design and answer the questions below. (15 pts.) Cohort Study (a) How would you select your study subjects-be specific about your enrollment criteria. (b) What variables would you measure and what type of analysis would you conduct? (c) How would you interpret an Attributable risk of 5% for this study? (d) What variables could be possible confounders for studying this association? (e) Name two ways to overcome confounding your results. (0) Name two advantages and two disadvantages of a cohort study design as compared to a case control study for this specifie investigation. Case-Control Study How would you select your study subjects-be specific about your enrollment criteria. (a) (b) What variables would you measure and what type of analysis would you conduct? (c) How would you interpret an Attributable risk of 5% for this study? (d) What variables could be possible confounders for studying this association? (e) Name two ways to overcome confounding your results. (0) Name two advantages and two disadvantages of a case-control study design as compared to a cohort study for this specific investigation. ohg

Explanation / Answer

A). Selection of study subjects:

The first step in developing a full study protocol is having a clear understanding of the research question to be answered.

The next step is to have explicit definitions of the independent and dependent variables of interest in the study. Then the target population can be defined. This process involves generation of a list of inclusion and exclusion criteria for potential study subjects.

Inclusion criteria define the type of subjects that full fill the needs of the researcher for the study. Common inclusion criteria include demographic parameters, clinical characteristics, geographic considerations, and the temporal setting.

B). Variables used to measure the criteria:

The MRC NSHD is a socially stratified birth cohort of 2547 women and 2815 men, with 19 follow-ups of the whole cohort between their birth in 1946 and age 43 years. Those interviewed (1634 men and 1628 women) at the age of 43 years were, in most respects, representative of the native-born population of that age. Loss to follow-up was due to death (7%), migration (11%), refusal (16%), and failure to trace (5%).

Blood pressure at 43 years was measured for 3157 cohort members by a team of trained nurses at interviews and examinations in the study member's home. Two measurements of blood pressure were taken using a Hawksley random zero sphygmomanometer with regular (12 × 23 cm) upper arm cuff.

A correction was made for arm circumference.26 The second measurement was used in analyses. Study members were asked whether they had taken any prescribed medicines or tablets for high blood pressure in the year preceding the interview.

C). Attributable risk :

Birthweight of cohort members, to the nearest quarter of a pound, was extracted from medical records within a few weeks of delivery and converted into kilograms. Heights and weights measured at 2, 4, 7, and 15 years, and at 43 years were used in analyses. Body mass index (BMI), defined as weight/height2, was calculated at each age.

All further analyses were carried out using standardized (sex-specific) birthweight and body size measures (z-scores), to allow easier comparison of the size of the effects at different ages. Since each of the potential confounding variables had missing data for a different subset of the sample, the association between birthweight and blood pressure was adjusted for each confounding variable one at a time. Tests for interaction between each confounding variable and birthweight were performed.

D). Variables could be possible for the confounders:

Infant's gestational age at birth.

This was based on maternal report of the last menstrual period and categorized as 23–27 weeks, 28–32 weeks, 33–34 weeks, 35–36 weeks, 37–42 weeks (full term), and ?43 weeks.

Infant's date of birth.

This was modeled as a continuous variable. We included this in order to adjust for age and for changes in perinatal care that may have occurred during the period that these study participants were born (1973–1979).

Infant's gender.

This variable was either female or male.

E). To overcome the confounder results:

A Confounder is a variable whose presence affects the variables being studied so that the results do not reflect the actual relationship. There are various ways to exclude or control confounding variables including Randomization, Restriction and Matching.

But all these methods are applicable at the time of study design. When experimental designs are premature, impractical, or impossible, researchers must rely on statistical methods to adjust for potentially confounding effects. These Statistical models (especially regression models) are flexible to eliminate the effects of confounders.

F). Advantage and disadvantages of comparison between cohort study and case study:

Advantages:

Gather data regarding sequence of events; can assess causality

Examine multiple outcomes for a given exposure

Disadvantages:

Large numbers of subjects are required to study rare exposures

Susceptible to selection bias

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