Question

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Much of what we know about the impact of food and diet on our health comes from large cohort studies such as the Nurses' Health Study and the Health Professionals Follow-Up Study. Briefly describe one advantage and one limitation to observational cohort studies.

Answer 1

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Explanation:-

Observational studies are an important category of study designs. To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct. Instead, observational studies may be the next best method to address these types of questions. Well-designed observational studies have been shown to provide results similar to randomized controlled trials, challenging the belief that observational studies are second-rate.

Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.

Advantage of Cohort Studies:-

Cohort studies are excellent for estimating the incidence and natural history of a condition. They may be prospective or retrospective and sometimes two cohorts are compared. They analyze predictors (risk factors) that enable relative risk calculation. Since they measure events in temporal sequence, they can distinguish causes from effects.

1. Allow Calculation of Incidence: Cohort studies allow you to calculate the incidence of disease in exposure groups, so you can calculate:

• Absolute risk (incidence)
• Relative risk (risk ratio or rate ratio)
• Risk difference
• Attributable proportion (attributable risk %)

2. Facilitate Study of Rare Exposures:

While a cohort design can be used to investigate common exposures (e.g., risk factors for cardiovascular disease and cancer in the Nurses' Health Study), they are particularly useful for evaluating the effects of rare or unusual exposures, because the investigators can make it a point to identify an adequate number of subjects who have an unusual exposure, e.g.,

• Exposure to toxic chemicals (Agent Orange)
• Adverse effects of drugs (e.g., thalidomide) or treatments (e.g., radiation treatments for ankylosing spondylitis)
• Unusual occupational exposures (e.g., asbestos, or solvents in tire manufacturing, )

Limitation of cohort studies:-

1. Expensive

2. Time-consuming

3. Inefficient for rare outcomes with long induction or latency periods

The main problem in observational cohort studies :- is the presence of confounders and selection bias (which are prevented in RCTs through randomization and blinding). A confounder can be defined as any factor that is related not only to the intervention (e.g. treatment) but also to the outcome and could affect both.One good example is age: in a study on the relationship between smoking (exposure) and lung cancer (outcome), age could be implicated as a factor that would increase the incidence of the outcome. Thus, if one of the groups (smokers or non-smokers) has an older population, the increase in lung cancer could be influenced by age (as a confounder), and not by the exposure studied.