An Introduction to the Fundamentals of Cohort and Case Control Studies PMC
Table Of Content
As seen in Figure 1, at the time of entry into the study (sampling of participants), some of the study participants have the outcome (cases) and others do not have the outcome (controls). During the study procedures, we will examine the exposure of interest in cases as well as controls. We will then study the association between the exposure and outcome in these study participants. Every now and then during clinical practice, we come across a case that is atypical or ‘out of the norm’ type of clinical presentation.
Community trial
Loss to follow-up is a situation in which the investigator loses contact with the subject, resulting in missing data. If too many subjects are loss to follow-up, the internal validity of the study is reduced. It is therefore important to select subjects who can be followed for the entire duration of the cohort study. To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct.
Bias
This blog summarizes the concepts of cluster randomization, and the logistical and statistical considerations while designing a cluster randomized controlled trial. On the other hand, cross-sectional studies collect data on a population at a single point in time. The goal here is to describe the characteristics of the population, such as their age, gender identity, or health status, and understand the distribution and relationships of these characteristics. This makes them very rigid and not generalisable, as no extrapolation can be made about other outcomes like risk recurrence or future exposure threat.
Determinants of defaulter to full vaccination among children aged 12–23 months in Siraro district, West Arsi zone ... - springermedizin.de
Determinants of defaulter to full vaccination among children aged 12–23 months in Siraro district, West Arsi zone ....
Posted: Fri, 01 Dec 2023 08:00:00 GMT [source]
Matching Cases and Controls
The use of incident cases is considered as preferential, as the recall of past exposure(s) may be more accurate among newly diagnosed cases. In addition, the temporal sequence of exposure and disease is easier to assess among incident cases. 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.
Blinding is especially important in studies where subjective response are considered as outcomes. This is because certain responses can be modified based on the knowledge of the experiment group that they are in. For example, a group allocated in the non‐intervention group may not feel better as they are not getting the treatment, or an investigator may pay more attention to the group receiving treatment, and thereby potentially affecting the final results.
Case-control and Cohort studies: A brief overview
People are often recruited because of their geographical area or occupation, for example, and researchers can then measure and analyse a range of exposures and outcomes. The strength of the association between an exposure and a disease in a case-control study can be measured using a few different statistical measures, such as odds ratios (ORs) and relative risk (RR). As pharmacotherapy experts, pharmacists are continually updating their knowledge about drug effects. In addition to being knowledge users of research findings, pharmacists increasingly play a larger role in observational studies of drug effects. Observational studies are inherently nonexperimental and, unlike randomized clinical trials (RCTs), do not involve any manipulation (such as randomization) of the treatment and control groups by the investigator. Case-control studies are prevalent in all fields of medicine from nursing and pharmacy to use in public health and surgical patients.
Source and study population
For instance, if we design a research protocol to study the association between metabolic syndrome (exposure) and psoriasis (outcome), we should ensure that we use the same criteria (clinically and biochemically) for evaluating metabolic syndrome in cases and controls. If we use different criteria to measure the metabolic syndrome, then it may cause information bias. In a case-control study, participants are selected for the study based on their outcome status. Thus, some participants have the outcome of interest (referred to as cases), whereas others do not have the outcome of interest (referred to as controls). Thus, by design, in a case-control study the outcome has to occur in some of the participants that have been included in the study.
A case-control study was conducted to investigate if exposure to zinc oxide is a more effective skin cancer prevention measure. The study involved comparing a group of former lifeguards that had developed cancer on their cheeks and noses (cases) to a group of lifeguards without this type of cancer (controls) and assess their prior exposure to zinc oxide or absorbent sunscreen lotions. This article describes the most common types of designs conducted by researchers. Cohort studies can assess a range of outcomes allowing an exposure to be rigorously assessed for its impact in developing disease. Additionally, they are good for rare exposures, e.g. contact with a chemical radiation blast.
Cases should be selected based on objective inclusion and exclusion criteria from a reliable source such as a disease registry. An inherent issue with selecting cases is that a certain proportion of those with the disease would not have a formal diagnosis, may not present for medical care, may be misdiagnosed or may have died before getting a diagnosis. Regardless of how the cases are selected, they should be representative of the broader disease population that you are investigating to ensure generalisability.
Retrospective cohort studies use existing secondary research data, such as medical records or databases, to identify a group of people with a common exposure or risk factor and to observe their outcomes over time. Case-control studies conduct primary research, comparing a group of participants possessing a condition of interest to a very similar group lacking that condition in real time. A cohort study compares the experience of 2 or more groups of patients who are followed concurrently forward in time (Figure 1).
Mothers of children who received folic acid supplementation during early pregnancy were significantly less likely to have a child with BDs. Mothers who did not receive folic acid supplementation during early pregnancy had a fourfold increased risk of having a child with BDs. This finding is consistent with studies conducted in Nigeria, Iraq, and Ethiopia, where folic acid supplementation was deficient [1, 17, 28].
If, for example, our cases of Kaposi's sarcoma came from across the country but our controls were only chosen from a small community in northern latitudes where people rarely go outside or get sunburns, asking about sunburn may not be a valid exposure to investigate. Similarly, if all of the cases of Kaposi's sarcoma were found to come from a small community outside a battery factory with high levels of lead in the environment, then controls from across the country with minimal lead exposure would not provide an appropriate control group. The investigator must put a great deal of effort into creating a proper control group to bolster the strength of the case-control study as well as enhance their ability to find true and valid potential correlations between exposures and disease states. One should not use the word case-control study for a randomised controlled trial (even though you have a control group in the study).
Nonetheless, matching may be useful to control for certain types of confounders. For instance, environment variables may be accounted for by matching controls for neighbourhood or area of residence. Household environment and genetic factors may be accounted for by enrolling siblings as controls. The next important point in designing a case-control study is the selection of control patients.
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