Example of a Population-based Case-Control Study: A better approach would be to select controls who were matched to the cases by neighborhood, age, and gender. An example of 1 would be a study of endophthalmitis following ocular surgery.
Sometimes researchers enroll multiple control groups. These factors would only matter if they impacted on the estimate of the proportion of the population who had diabetes. A population-based case-control study is one in which the cases come from a precisely defined population, such as a fixed geographic area, and the controls are sampled directly from the same population.
The practical value of producing rapid results or investigating rare outcomes may outweigh the limitations of case-control studies. It may be difficult for some people to recall all these details accurately.
Results from observational studies are often criticized for being vulnerable to influences by unpredictable confounding factors.
Within what period of time after operation will the development of endophthalmitis qualify as a case — one day, one week, or one month? Because of their efficiency, they may also be ideal for preliminary investigation of a suspected risk factor for a common condition; conclusions may be used to justify a more costly and time-consuming longitudinal study later.
Population controls may also be more difficult to obtain, however, because of lack of interest in participating, and there may be recall biassince population controls are generally healthy and may remember past exposures less accurately.
Analysis; Odds Ratios and Confidence Intervals In the analysis stage, calculate the frequency of each of the measured variables in each of the two groups.
Advantages and Disadvantages Advantages. In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature. This is known as recall bias. For statistical reasons, however, there is little gained by including more than two controls per case.
Risk Factors and Sampling Another use for case-control studies is investigating risk factors for a rare disease, such as uveal melanoma. Consider a case-control study intended to establish an association between the use of traditional eye medicines TEM and corneal ulcers.
For example, if the cases are women with cervical cancer who have been referred from all over the state, it would be inappropriate to use controls consisting of women with diabetes who had been referred primarily from local health centers in the immediate vicinity of the hospital.
By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures.
Clinical criteria must be identified in great detail. Over-matching can make it difficult to find enough controls. In this situation the statistical power of the study can be increased somewhat by enrolling more controls than cases.
For example, cases with a certain disease might be referred to a particular tertiary hospital for specialized treatment. To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct.
Cross-sectional studies, also known as prevalence studies, examine the data on disease and exposure at one particular time point Figure 2. However, the additional power that is achieved diminishes as the ratio of controls to cases increases, and ratios greater than 4: If cases are obtained from a medical facility, the comparison groups should be obtained from the same facility, provided they meet two criteria: Methods of Control Sampling There are three strategies for selecting controls that are best explained by considering the nested case-control study described on page 3 of this module: In this example, cases might be recruited by using hospital records.
Since case-control studies start with people known to have the outcome rather than starting with a population free of disease and waiting to see who develops it it is possible to enroll a sufficient number of patients with a rare disease.
Advantages of Case-Control Studies Case-control studies have specific advantages compared to other study designs. Care must be taken to be objective in the search for past risk factors, especially since the outcome is already known, or the study may suffer from researcher bias.
In this situation cases might be identified from a state cancer registry, for example, and the comparison group would logically be selected at random from the same source population. Similarly, it would be inappropriate to use patients from the emergency room, because the selection of a hospital for an emergency is different than for cancer, and this difference might be related to the exposure of interest.
The temporal relationship between the supposed cause and effect cannot be determined by a case-control study.Hospital or Clinic Controls: The advantages of using controls who are patients from the same facility are: Since case-control studies are often used for uncommon outcomes, investigators often have a limited number of cases but a plentiful supply of potential controls.
If b and d (from the case-control study) are sampled from the source population, n1 + n2, then b will represent the Hospital controls - There are certain problems with of the same problems as hospital controls.
Advantages of case-control studies. Advantages of case control studies (3) 1) Reduces number of people needing to be studied Same eligibility criteria as case group 3) Controls need to be as similar to case group as possible, i.e.
from same hospital/community. Random Sampling.
Sampling where people are identified from a list of all potential participants. Epidemiology in Practice: Case-Control Studies. Susan Lewallen, MD and Paul Courtright, Case-control studies have specific advantages compared to other study designs.
They are comparatively quick, inexpensive, and easy. These could include a set of community controls and a set of hospital controls. Start studying Cohort and Case-Control Studies. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
Disadvantages Hospital-Based Controls. Potential for selection bias, less generalizable Advantages of Case-Control Design. Keywords: observational studies, case-control study, cohort study, Thus in comparison to cohort studies, case-control studies are quick, matched by age and sex in the same hospital and same period.
Controls were of Hans Chinese origin from Jiangsu, China, the same area from where the cases were selected.Download