Pharmacoepidemiology (article)

11 important questions on Pharmacoepidemiology (article)

What is the problem with spontaneous reporting systems?

It is impossible to calculate the frequency of ADRs directly and to compare risks between drugs. Because the reporting is not always in the same rate pharmacoepidemiology studies are needed.

What three main issues does pharmacoepidemiology address?

1) What is the drug use in a specific population?
2) What are the determinants of drug use? (factors that determine drug choice)
3) What are the outcomes of drug use (beneficial and adverse effects)?

How can selection bias occur in a case-control study and in a cohort study?

case-control study: selection bias may occur due to the fact that a case group and a control group have to be selected. The Odds ration can be overestimated in this case.
retrospective cohort studies: Selection bias may occur when the selection of exposed and unexposed individuals is based on different criteria that are related to the outcome of interest.
In prospective cohort studies selection bias is unlikely.
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What may be a result of bias?

Different odds ratios. When the inaccuracy for both groups is the same the risk estimate will become diluted and the risk estimate will be closer to 1 than that it would have been had the data been completely accurate.  This is called non-differential misclassification.

To what criteria must a determinant met will it be a confounding?

- it is an independent predictor (although not necessarily a cause) for the occurrence of the disease.
- Is associated with the exposure of interest
- Must not be an intermediate link in the causal pathway between exposure and outcome.

What are the characteristics, advantages and disadvantages of a cohort and a case-control study?

Case control: - usually small numbers, disease oriented, relatively quick and inexpensive, multiple exposures can be studied, no direct calculation of incidence, prone to bias, temporal relationship difficult to establish and efficient for rare diseases.

cohort study: usually large populations, exposure oriented, relatively expensive and time consuming, multiple effects can be studied, incidence can be calculated, less prone to bias especially if it is prospective but risk of loss to follow-up, temporal relationship can be assessed,and efficient for rare exposures.

What is the difference between cumulative incidence and the incidence density?

With cumulative incidence the denominator is the number of people in the population at risk at the beginning of a time period.
With the incidence density only new cases are incorporated in the numerator and the actual person-time at risk is used in the denominator.
So the incidence density is the number of new cases of a disease during a given time period, divided by the total person time of observation.

What are descriptive studies?

These studies describe patterns of drug utilization in relation to variables such as disease, gender, place and time.

What are case-control studies?

These are analytical epidemiological investigations in which subjects are selected on the basis of whether they do (cases) or do not (controls) have a particular disease under study. The groups are then compared with respect to the proportion having or not having been exposed to the drug of interest.

What are cohort studies?

In these a group or groups of individuals are identified on the basis of the presence or absence of exposure to a drug as a suspected risk factor for the disease. At the time that exposure status is established, all subjects must be free from the disease under study. These studies can be prospective and retrospective.

What formulas are use to calculate risk estimates in cohort studies and case-control studies?

cohort: a relative risk: RR = IncidenceExp/incidenceUnexp
case-control: Odds ratio: ad/bc. (a = exposed + disease, b = only exposed, c= only disease, d = no disease and no exposure)

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