Question

please answer in depth.

1. What is a cohort study? 2. How are cohorts selected? 3. In the Scottish Heart Study case study, does dietary fiber appear to be more protective against CHD risk or against non-CHD death? 4. The authors do not detail the causes of the 'non-CHD death.' Speculate about what those causes could be and what they might have to do with dietary fiber. 5. If the 95 percent confidence interval for CHD case' was (8.1, 9.6) instead of (8.1, 8.6), how would it affect the conclusions? 6. How is incidence measured? 7. In the Smoking and Prostate cancer case study, what is the odds ratio for the risk of prostate cancer with smoking? 8. What are the sampling fractions for exposed and unexposed controls? What are the advantages and disadvantages of cohort studies?

Answer 1

1)A cohort study is a particular form of longitudinal study that samples a cohort,performing a cross section at intervals through time.

2)Cohort studies begin with the selection of a group or population that will be followed to document their outcomes at later times.Information is gathered about different exposures and/or risk categories of the cohort .once data is collected,the cohort is usually divided based on exposure or risk category.characteristics of the cohort must be carefully defined and recorded to maintain an accurate study.

3)Dietary fiber shows to be protective against CHD risk and death.Those who had CHD had a lower fiber intake than those who had no event.Those who died from a cause other than CHD had a lower fiber intake than those with no event.

4)Non-CHD deaths could be caused by cancer or cerebrovascular disease.fiber level may be protective for mortality from these causes.

5)The study would show that the fiber intake level of CHD cases was not statistically significantly different from the fiber intake level of those without an event.

6)Incidence is measured by dividing the number of subjects who develop a disease by the total number of subjects in the cohort.Another way is to calculate incident in terms of density such as person-years or person-months of exposure.incidence density is an incidence rate where the denominator is expressed in a person-time metrics,such as person-years.

7)Odd ratio is 0.9

8)The sampling fraction of exposed controls would be 250/501,375=0.00050.The sampling fractions of unexposed controls would be 250/1,671,250-501,375=0.000214.

Cohort study can calculate incidence and relative risk directly rather than by estimate.They can give an exact time frame.Bias is less of a problem since exposures are systematically and regularly documented.The cohort design can also be used to study multiple outcomes or multiple exposures.