Case control study epidemiology ppt
One starts by identifying diseased subjects and determines their exposure distribution; one then takes a sample of the source population that produced those cases in order to estimate the exposure distribution in the overall source population that produced the cases.
She then consulted her personal physician, who performed a thorough evaluation. However, the most important factor to the quality of evidence these studies provide, is their methodological quality. These studies differ from clinical investigations in that individuals have already been administered the drug during medical treatment or have been exposed to it in the workplace or environment.
They are usually conducted on data that already exists from prospective studies and the exposures are defined before looking at the existing outcome data to see whether exposure to a risk factor is associated with a statistically significant difference in the outcome development rate.
Cohort study design. Case-control studies are particularly useful when the outcome is rare is uncommon in both exposed and non-exposed people. Bias Errors Epidemiologists attempt to control errors that can occur in the collection of data, which are known as bias errors.
The probability that an event will occur is the fraction of times you expect to see that event in many trials.
Recall bias occurs when individuals are asked to remember exposures or conditions that existed years before. Information bias, which occurs when study subjects are misclassified as to disease or exposure status.
Therefore, you cannot calculate risk ratio or risk difference.
Case control study pdf
Whilst cohort studies are useful, they can be expensive and time-consuming, especially if a long follow-up period is chosen or the disease itself is rare or has a long latency. More specifically, the control population used as a comparison group must be as similar as possible to that of the test group, for example, same age, sex, race, social status, geographical area, and environmental and lifestyle influences. Postmarketing Studies Finally, for consumer products, postmarketing epidemiological studies can be performed. The statistical ability to detect an effect. The three main types of bias errors are: Selection bias, which occurs when the study group is not representative of the population from which it came. To gain precision, the study and control populations should be as large as possible. If the probability of an event occurring is Y, then the probability of the event not occurring is 1-Y. She then consulted her personal physician, who performed a thorough evaluation. Case-control and Cohort studies: A brief overview Posted on December 6, by Saul Crandon Tutorials and Fundamentals Introduction Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence. Study Design When designing an epidemiology study, the most critical aspects include: An appropriate control group. In other words, I don't know the exposure distribution for the entire source population. Table 1. Knowledge Check While animal testing was historically the primary method used in testing for toxicity, modern testing methods prefer: Correct! So, I can't compute the probability of disease in each exposure group, but I can compute the odds of disease in each group. Cohort studies Cohort studies can be retrospective or prospective.
On physical examination, she had mild, diffuse muscle tenderness and a mild, erythematous maculopapular rash over much of her body. In the example above the case-control study of only 79 subjects produced an odds ratio 6.
Postmarketing Studies Finally, for consumer products, postmarketing epidemiological studies can be performed.
Case control and cohort study ppt
This can suggest associations between the risk factor and development of the disease in question, although no definitive causality can be drawn. In a case-control study there is no "follow-up" period. Case-control study design. Eosinophilia-myalgia syndrome EMS was diagnosed. If sampling of cases, controls, or both is influenced by prior exposure history, then a selection bias may be present. Whilst cohort studies are useful, they can be expensive and time-consuming, especially if a long follow-up period is chosen or the disease itself is rare or has a long latency. Epidemiological studies measure the risk of illness or death in an exposed population compared to that risk in an identical, unexposed population for example, a population the same age, sex, race and social status as the exposed population.
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