In a study that is designed and conducted as a case-control study, you cannot calculate incidence. The selected control group must be at similar risk of developing the outcome; it would not be appropriate to compare a group of controls who had traumatic corneal lacerations with cases who underwent elective intraocular surgery.
However, the small control sample of non-diseased subjects gives me a way to estimate the exposure distribution in the source population. Will those differences cloud the study outcomes?
Consider a case-control study intended to establish an association between the use of traditional eye medicines TEM and corneal ulcers. In theory, the case-control study can be described simply. Preferably controls are drawn from the same population as the cases. 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.
It was later shown by Miettinen in that this assumption is not necessary and that the odds ratio of exposure can be used to directly estimate the incidence rate ratio of exposure without the need for the rare disease assumption.
These studies are designed to estimate odds. Within what period of time after operation will the development of endophthalmitis qualify as a case — one day, one week, or one month?
A most critical and often controversial component of a case-control study is the selection of the controls. Matching Cases and Controls Although controls must be like the cases in many ways, it is possible to over-match. An example of 2 would be a study of risk factors for uveal melanoma, or corneal ulcers.
How will sterile inflammation be differentiated from endophthalmitis? A discordant pair occurs when the exposure status of case is different than the exposure status of the control. Numbers of cases and controls do not have to be equal.
We have selected cases and controls from a population, often an unknown population. By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures.
Fictitious Example There is a suspicion that zinc oxide, the white non-absorbent sunscreen traditionally worn by lifeguards is more effective at preventing sunburns that lead to skin cancer than absorbent sunscreen lotions.A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest).
In theory, the case-control study can be described simply. First, identify the cases (a group known to have the outcome) and the controls (a group known to be.
They can determine if there is an associational relationship between condition and risk factorExample: A study in which colon cancer patients are asked what kinds of food they have eaten in the past and the answers are compared with a selected control mint-body.com control studies are less reliable than either randomized controlled trials or.
1 STROBE Statement—Checklist of items that should be included in reports of case-control studies Item No Recommendation Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract (b) Provide in the abstract an informative and balanced summary of what was done and what was found Introduction.
A case-control design offers an alternative that is much more efficient. The goal of a case-control study is the same as that of cohort studies, i.e. to estimate the magnitude of association between an exposure and an outcome.
Case Control Study Definition A study that compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls), and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk.
While a case-control study design offers less support for a causation hypothesis than the longer and more expensive cohort design, it does provide stronger evidence than a cross-sectional study.
Below is a 2 × 2 table for case-control data.Download