In designing a study of occupational injury and risks arising from longterm illness and prescribed medication, we lacked data on subjects occupation, without which employed cases typically in manual occupations would. Reducing selection bias in casecontrol studies from rare. In this paper, a theoretical framework for selecting controls in case control studies is developed. 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. Download citation automating the selection of controls in case control studies a case control study is an observational study in which subjects are classified according to the presence cases. A synthesis of classical and recent thinking on the issues involved in selecting controls for case control studies is presented in this and two companion papers s. Analysis of case control studies the odds ratio or is used in case control studies to estimate the strength of the association between exposure and outcome.
Casecontrol studies of potential protection against colorectal cancer associated with nonsteroidal antiin. Objectives it has been argued that in casecontrol studies, controls should be drawn from the base population that gives rise to the cases. Case control study cohort study medical humanities. Describe methods of accrual of cases and controls 5. Results are presented using methods of kelsey, fleiss, and fleiss with a continuity. The next important point in designing a casecontrol study is the selection of control patients.
In most case control studies the hardest decision is the choice of the control group, as in the ideal control group the proportion exposed is the same as in the population that produced the cases. Controls can be taken from known or unknown study populations. Efficiency of casecontrol studies with multiple controls per case. Topics covered include matching, control case ratio, choice of nested case control or casecohort design, twostage sampling, and other methods that can be used for control selection. Successful investigation of national outbreaks of communicable disease relies on rapid identification of the source. A known group consists of a defined population observed over a period, such as passengers on a cruise ship.
In this design, participants are selected for the study based on their outcome status. Remember that in a case control study the controls are used to estimate the exposure distribution i. Case control studies unc gillings school of global. During a national prospective case control study from july. The strength of casecontrol studies can be appreciated in early research done by investigators hoping to understand the cause of aids. In casecontrol studies conducted using computerized databases, controls are often selected as a random sample from the base population. Casecontrol studies a case control study involves two populations cases and controls and has three distinct features.
In the limit, it will be the indicator that can measure validity. Casecontrol studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that conditiondisease the. In casecontrol studies, controls estimate the frequency of an exposure in the population under study. Casecontrol methodologies are commonly used to achieve this. Epidemiologic study designs jacky m jennings, phd, mph. Introduction of casecontrol study aug, 5, 2014 hirohide yokokawa, m. In our second paper 1, we apply the principles presented in this paper to the selection of control groups used in casecontrol studies, including population controls, hospital controls, medical practice controls, friend controls, and relative controls.
Selection of controls in casecontrol studies american. Case control studies are prone to bias and confounding. Avoidance of bias is important when choosing controls for a casecontrol study. A comparison of two control groups in a case control study of the efficacy of bcg revaccination. Casecontrol studies identified risk groupseg, homosexual men, intravenous drug users, and bloodtransfusion recipientsand risk factorseg, multiple sex partners, receptive anal intercourse in homosexual men, and not using. Cases and controls are patients who are hospitalized or outpatients. Selection of suitable controls is an important aspect of casecontrol studies because if there is a systematic difference between cases and controls in any aspect other than the disease itself selection bias, a true association between the exposure and disease may be missed or a spurious association observed. Analysis of casecontrol studies the odds ratio or is used in casecontrol studies to estimate the strength of the association between exposure and outcome. Introduction a casecontrol study is designed to help determine if an exposure is associated with an outcome i. Note that it is not possible to estimate the incidence of disease from a case control study unless the study is population based and all cases in a defined population are obtained. Casecontrol studies advantages good design for rare, chronic and long. A casecontrol study also known as casereferent study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. You enter the desired confidence level, power, a hypothetical percentage of exposure among the controls, and either an odds ratio or a hypothetical percentage of exposure among the cases.
In fact, wacholder and colleagues have extensively discussed aspects of design of case control studies and selection of controls in their article. First, identify the cases a group known to have the outcome and the controls a group known to be free of the. We assessed control selection methods used in recently published casecontrol studies for methodological and resource issues to determine if a standard approach could be identified. Use of control comparison groups is a powerful research tool. Casecontrol studies e r i c n o t e b o o k s e r i e s casecontrol studies are used to determine if there is an association between an exposure and a specific health outcome. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Selection of controls in macmahons casecontrol study of pancreatic cancer included. The basic premise of such studies is the comparison of two groups. Note that it is not possible to estimate the incidence of disease from a casecontrol study unless the study is population based and all cases in a defined population are obtained. As noted above, it is always useful to think of a case control study as being nested within some sort of a cohort, i. Case control study design is a type of observational study. Casecontrol studies offer an efficient observational analytic design, but they also carry a high potential for the introduction of bias. It uses a control or comparison group to support or refute an inference.
Several design options available in the planning stage of case control studies are examined. Topics covered include matching, controlcase ratio, choice of nested casecontrol or casecohort design, twostage sampling, and other methods that can be used for control selection. Usually, cases are people with disease, but treatment outcomes or other criteria can be used to define a case. Automating the selection of controls in casecontrol studies. Casecontrol study an overview sciencedirect topics. Overview of casecontrol studies in a casecontrol study with 2 groups, one group has the disease of interest cases and a comparable group is free from the disease controls casecontrol study identifies possible causes of disease by find out out how the 2 groups differ wrespect to exposure of some factor. Two related studies, a casecontrol study in which multiple control groups were employed and a 15year cohort study of all cases and controls, provided an opportunity to compare controls selected at.
Topics covered include matching, controlcase ratio, choice of nested case. Robins j, pike m 1990 the validity of casecontrol studies with nonrandom selection of controls. Established methods of recruiting population controls for casecontrol studies to investigate gastrointestinal disease outbreaks can be time consuming, resulting in. Control selection methods in recent casecontrol studies conducted as part of infectious disease outbreaks. Casecontrol studies compare cases and diseasefree controls for their exposure status and compare the risk of exposure in cases and controls. While traditional casecontrol studies can be subject to selection bias and exposure recall bias, the nested casecontrol design is less prone to these biases, due to cases and controls being. Selection of controls that are identical to cases with respect to one or more potentially confounding factors. Control selection methods in recent casecontrol studies.
Challenges in casecontrol studies selection of controls sample size matching group or individual selection of cases. Case control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition the cases with patients who do not have the condition but are otherwise similar the controls purpose of case control studies 1. These types of studies are common in public health and medical research. This item assesses whether the control series used in the study is derived from the same population as the cases and essentially would have been cases had the outcome been present. Bypassing the selection rule in choosing controls for a. Cases and controls are registered in a cohort study. Pdf control selection methods in recent casecontrol. Openepi sample size for unmatched casecontrol studies. Selecting cases and controls from the source cohort without knowledge of their exposure status.
Cases and controls are patients who are hospitalized or. Selection bias arises if controls are not representative of those at risk of the disease in question. This work is licensed under a creative commons attribution. Selection of controls in database casecontrol studies. This representative choice of controls is intended to guard against selection bias. Cohort studies and casecontrol studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures. Even with representative cases and controls, if there is a high or differential nonparticipation rate among or between cases and controls, selection bias may be introduced. All other patients who were under the care of the same physician in the same hospital at the time of the interview of a patient with pancreatic cancer excluded. In this paper, a theoretical framework for selecting controls in casecontrol studies is developed. A synthesis of classical and recent thinking on the issues involved in selecting controls for casecontrol studies is presented in this and two companion papers s. A case control study is a type of study design in epidemiology.
Department of epidemiology, university of pittsburgh, pa 15261. In theory, the case control study can be described simply. In a case control study selection bias occurs when subjects for the control group are not truly representative of the population that produced the cases. Purpose of casecontrol study major types of casecontrol studies procedure of casecontrol study risk assessment in casecontrol study example of casecontrol study. Mandep a synthesis of classical and recent thinking on the issues involved in selecting controls for case control studies is presented in this and two companion papers s. Several design options available in the planning stage of casecontrol studies are examined. Selection of controls for clinical research studies in.
The selection of cases and controls seems to be the most difficult question in planning and conducting a casecontrol study and remains essential regarding the practical requirements for all the steps of this kind of epidemiological design. Yes no statin 20 1,000 1,020 no statin 80 9,000 9,080 100 10,000 10,100 rr 20 1,020 80 9,080 2. Casecontrol studies begin at the end outcome is the basis to select the comparison groups they test hypotheses concerning the association and magnitudes of a relationship between outcomes and exposures the strength of association is measured by an odds ratio or which is a good proxy for a relative risk when disease is rare. We show, using data from a database casecontrol study, that such a definition of controls may also lead to selection bias under two conditions. In view of this there are two key principles that should be followed in selecting controls. One group was selected from subjects presenting to the heath unit the. The application of casecontrol matching methodology results in cohorts of cases i. Both exposure and outcome have occurred before the start of the study. This module calculates sample size for an unmatched casecontrol study. Define eligibility criteria for cases and controls 4.
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