In a cohort study, starting the study by selecting a defined population before any of its members become exposed, rather than starting by selecting exposed and unexposed individuals, is an advantage because:

A. The study can be completed more rapidly
B. A number of outcomes can be staudied simultaneously
C. A number of exposure can be staudied simultaneouslyD. The study will cost less to carry out
E. A and D

Explanation:

A cohort refers to a group of organisms which share a defined characteristic.

Cohort study involves study of these cohorts and gathering data at particular interval of time.

In cohort study, a group of individual with same characteristic are chosen and certain data such as their life history, advent of disease and their effect are recorded.

Cohort study can be defined as a longitudinal study because it involves the repeated observation of same factor again and again..

Cohort studies do not involve any control set up. It provides an advantage by allowing to study the effect of a number of exposures simultaneously.

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oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%