Question

In cohort studies of the roles of a suspected factor in the etiology of a disease, it is essential that: There be equal numbers of persons in both study groups At the beginning of the study, those with the disease and those without the disease have equal risks of having the factor The study group with the factor and the study group without the factor be representative of the general population The exposed and nonexposed groups under study be as similar as possible with regard to possible confounding factors Both b and c

Answer 1

Solution:

The cohort studies are classified into two types,which include prospective cohort study and retrospective cohort study.

Retrospective cohort study is also called historic study.

it involves study of group of individuals that share common exposure factor.

it is used to study the influence of factor on development of a disease .in this method ,the information from the past records is collected in this method the study groups include both exposed and nonexposed.

in prospective cohort study, a group of individuals who differ in certain factors are studied over time to determine the effect of factors on rates of outcome.

The advantages of cohort studies are as follows:

• it clearly indicates the temporal sequence
• it allows the calculation of incidence in exposure groups
• it facilitates the study of rare exposures
• allows examination of multiple effects of single exposure ,thus many disease outcomes can be studies simultaneously
• it reduces the possibility of results to be biased

Thus .the options a,b, c and e are in correct.

confounding factor is the factor that correlates with both dependent factors to exp;lain correlation between two factors . Thus ,in cohort studies to understand the role of suspected factor in etiology of disease is that both exposed and nonexposed groups should be as similar as possible with regard to confounding factors.

Hence the correct answer is option D