#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? (e) Name two ways to overcome confounding your results. (f) Name two advantages and two disadvantages of a cohort study design as compared toa case control study for this specific investigation. Case-Control 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. Name two advantages and two disadvantages of a case-control study design as compared to a cohort study for this specific investigation.

Explanation / Answer

Ans

1. Cohort study is medical research which is used to investigate the causes of disease and to links between the risk factors and health outcomes. It is mainly of two types prospective and retrospective. Cohort study design is best scientific method to measure the effects of a suspected risk factor. In prospective study, researcher raise a question and form hypothesis about the cause of disease, for the sake of this group of subject (low body weight and high BP problem in late 40 s) are observed and relevant data is collected to the concerned disease. By this way any change in health can be detected and possible risk factors can be identified. For example, specific lifestyle details could be ask by patients to record for the course of study and can analyzed the possible correlations between the lifestyle factors and disease.

2. Cohort study is used to estimate the risk of disease, the incidence rate and relative risks. Cases are studied from a defined population, current exposure status and onset of disease observed in the subjects over time. Cohort design is of two types prospective, retrospective.

Variables in cohort study are measured by stastical analysis and regression analysis.

3.With the cohort study - states that low body weight during fetal life develops risk factors, such as high blood pressure, for cardiovascular (BP problems) disease in age 40. Many studies suggest the association between birthweight and systolic blood pressure (SBP), these studies suggest a reasonable valid conclusion for the study. Pregnancy related factors for the birthweight–blood pressure association is not clear it is concerned that the association are related with the lifetime socioeconomic problems. The birthweight reflects the postnatal rather fetal growth, if negative association emerges after adjusting the body. It is also studied that there may be influence on postnatal growth on blood pressure with respective to fetal growth. Fetal growth can be investigated with relation to childhood blood pressure, early adult blood pressure or treatment used for hypertension in adulthood. With the help of this study both prenatal growth in relation to middle age and BP problems in later stages can be investigated.

4.In a cohort study, the unexposed subjects has same characteristics as the exposed subjects.

Formula for a logistic regression is: ln?(p/(1 ? p)) = ? + ? 1?X 1 + ? 2?X 2 + ?+? n?X n, to study the cofounders.

5. Analyses can carried out for systolic and diastolic blood pressure at 40-50 years by using regression .For the study of fetal body weight model proposed by Lucas et al can be used to investigate the hypothesis. Other analysis can be carried out by standardized (sex-specific) birthweight and body size measures (z-scores), to allow easy comparison of weight effect at different ages. And the cofounding variables are adjusted for the subsets of the subjects and to test the association between birthweight and blood pressure Tests for interaction can be performed for the confounding variable and birthweight. Regression analysis is also prescribed for the effect of birth weight on blood pressure which was mediated through the childhood growth.

To assess the childhood growth influenced by blood pressure is independent of the birthweight, differences between the z-scores in birthweight and both z-scores in BMI and height can be calculated, and a model including birthweight and growth variables can be studied.

6. Disadvantage and Advantage of cohort study designs:

   Advantage:

Disadvantage:

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