A. Selection of Cases and Controls The first is to identify a suitable group of cases and a group of controls. While the identification of cases is relatively easy, the selection of suitable controls may present difficulties.
What are the controls in a case-control study?
Case-control studies should include two groups that are identical EXCEPT for their outcome / disease status. As such, controls should also be selected carefully. It is possible to match controls to the cases selected on the basis of various factors (e.g. age, sex) to ensure these do not confound the study results.
What is the difference between a case and a control?
Design 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).
How do you choose a control group for a case study?
When designing a case-control study, the researcher must find an appropriate control group. Ideally, the case group (those with the outcome) and the control group (those without the outcome) will have almost the same characteristics, such as age, gender, overall health status, and other factors.
What is a case control design in research?
Case-Control study design is a type of observational study. In this design, 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).
Why are cases and controls matched?
Matched case-control study designs are commonly implemented in the field of public health. While matching is intended to eliminate confounding, the main potential benefit of matching in case-control studies is a gain in efficiency.
How many controls are in a case-control study?
Investigators planning case-control studies are usual- ly advised to include no more than four or five controls per case because little statistical power is gained by fur- ther increasing this ratio (1,2).
What are cases vs controls?
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls).
What principles should we follow when selecting controls?
They proposed and summarized four basic principles: study base, deconfounding, comparable accuracy and efficiency.
How do you design a case-control?
Five steps in conducting a case-control studyDefine a study population (source of cases and controls) ... Define and select cases. ... Define and select controls. ... Measure exposure. ... Estimate disease risk associated with exposure. ... Confounding factors. ... Matching. ... Bias.
How do you match a case-control study?
In a matched study, we enroll controls based upon some characteristic(s) of the case. For example, we might match the sex of the control to the sex of the case. The idea in matching is to match upon a potential confounding variable in order to remove the confounding effect.
How many groups are in a case-control study?
A case-control study is a type of observational study where researchers analyze two groups of people (cases and controls) to look at factors associated with particular diseases or outcomes.
What is the main purpose of selecting controls in a case-control study?
The purpose of the control group is to determine the relative size of the exposed and unexposed components of the source population.
What are controls in case-control study?
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). The investigator then assesses the exposure in both these groups.
What is an example of a case-control study?
For example, investigators conducted a case-control study to determine if there is an association between colon cancer and a high fat diet. Cases were all confirmed colon cancer cases in North Carolina in 2010. Controls were a sample of North Carolina residents without colon cancer. The odds ratio was 4.0.
What is the source population for a case-control design?
The source population is the population that gives rise to the cases included in the study. If a cohort study were undertaken, we would define the exposed and unexposed cohorts (or several cohorts) and from these populations obtain denominators for the incidence rates or risks that would be calculated for each cohort.
What are controls for a case-control study quizlet?
A study in which cases of disease are identified, and then a sample of the population that produced the cases is identified (the controls). Exposures are determined and compared for individuals in each group. You compare exposures in cases and controls.
What are the factors that determine how controls are to be similar to the cases?
Controls. Controls should be chosen who are similar in many ways to the cases. The factors (e.g., age, sex, time of hospitalisation ) chosen to define how controls are to be similar to the cases are the ‘matching criteria’.
Why is case control retrospective?
By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures. When the subjects are enrolled in their respective groups, the outcome of each subject is already known by the investigator. This, and not the fact that the investigator usually makes use ...
What are the advantages of case control studies?
Case-control studies have specific advantages compared to other study designs. They are comparatively quick, inexpensive, and easy. They are particularly appropriate for (1) investigating outbreaks, and (2) studying rare diseases or outcomes.
Is a case control study a case control study?
All studies which contain ‘cases’ and ‘controls’ are not case-control studies. One may start with a group of people with a known exposure and a comparison group (‘control group’) without the exposure and follow them through time to see what outcomes result, but this does not constitute a case-control study.
The Nature of Case-Control Studies
By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures. When the subjects are enrolled in their respective groups, the outcome of each subject is already known by the investigator.
Steps Involved in Case-Control Studies
By definition, a case-control study involves two populations – cases and controls.
A. Selection of Cases and Controls
The first is to identify a suitable group of cases and a group of controls.
B. Matching
The controls may differ from the cases in a number of factors such as age, sex, occupation, social status, etc.
C. Measurement of Exposure
Definitions and criteria about exposure (or variables which may be of aetiological importance) are just as important as those used to define cases and controls.
Limitations of Case-Control Study
Problems of bias relies on memory or past records, the accuracy of which may be uncertain; validation of information obtained is difficult or sometimes impossible.
Why is case control important?
Case-control studies are useful to study the association of risk factors and outcomes in outbreak investigations.
Why is individual matching important in case control studies?
Matching is a useful technique to increase the efficiency of study . ’Individual matching’ is one common technique used in case-control study.
Why is match used in case control studies?
Matching is often used in case-control control studies to ensure that the cases and controls are similar in certain characteristics, and it is a useful technique to increase the efficiency of the study.
Is a case control study an experimental study?
A randomised controlled trial is an experimental study. In contrast, case-control studies are observational studies. These are two different groups of studies. One should not use the word case-control study for a randomised controlled trial (even though you have a control group in the study).
Is a control group a case-control study?
Every study with a control group is not a case-control study. For a study to be classified as a case-control study, the study should be an observational study and the participants should be recruited based on their outcome status (some have the disease and some do not).
What is a case control study?
Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence. These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1). Although these studies are not ranked as highly as randomised controlled trials, they can provide strong evidence if designed appropriately.
What is inherent issue with selecting cases?
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.
Why are prospective cohort studies more common?
This is one of their important strengths. 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.
Why are cohort studies important?
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.
Is a case control study observational?
Both case-control and cohort studies are observational, with varying advantages and disadvantages. However, the most important factor to the quality of evidence these studies provide, is their methodological quality.
Is case control biased?
Nevertheless, as case-controls are retrospective, they are more prone to bias. One of the main examples is recall bias. Often case-control studies require the participants to self-report their exposure to a certain factor.
Is a cohort study the same as a case study?
Cohort studies. Cohort studies can be retrospective or prospective. Retrospective cohort studies are NOT the same as case-control studies. In retrospective cohort studies, the exposure and outcomes have already happened. They are usually conducted on data that already exists (from prospective studies) and the exposures are defined ...
Why is case control important?
Because of these advantages, case-control studies are commonly used as one of the first studies to build evidence of an association between exposure and an event or disease. In a case-control study, the investigator can include unequal numbers of cases with controls such as 2:1 or 4:1 to increase the power of the study.
Why are case control studies used?
Case-control studies, due to their typically retrospective nature, can be used to establish a correlationbetween exposures and outcomes, but cannot establish causation. These studies simply attempt to find correlations between past events and the current state.
Why do investigators need to create a 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.
What are the characteristics of a case group and a control group?
Ideally, the case group (those with the outcome) and the control group (those without the outcome) will have almost the same characteristics, such as age, gender, overall health status, and other factors. The two groups should have similar histories and live in similar environments.
What are the advantages of case control?
Advantages. There are many advantages to case-control studies. First, the case-control approach allows for the study of rare diseases. If a disease occurs very infrequently, one would have to follow a large group of people for a long period of time to accrue enough incident cases to study. Such use of resources may be impractical, so ...
What is case control study?
A case-control study is a type of observational study commonly used to look at factors associated with diseases or outcomes. The case-control study starts with a group of cases, which are the individuals who have the outcome of interest.
What is the potential for failing to identify confounding variables or exposures?
Similarly, the researcher must recognize the potential for failing to identify confounding variables or exposures, introducing the possibility of confounding bias, which occurs when a variable that is not being accounted for that has a relationship with both the exposure and outcome.
What is the purpose of case control study?
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. However, case-control studies employ a different sampling strategy that gives them greater efficiency.
What is population based case control?
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. 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. Population controls can be identified from voter registration lists, tax rolls, drivers license lists, and telephone directories or by "random digit dialing". Population controls may also be more difficult to obtain, however, because of lack of interest in participating, and there may be recall bias, since population controls are generally healthy and may remember past exposures less accurately.
Why are cohort studies problematic?
Cohort studies have an intuitive logic to them, but they can be very problematic when one is investigating outcomes that only occur in a small fraction of exposed and unexposed individuals. They can also be problematic when it is expensive or very difficult to obtain exposure information from a cohort. In these situations a case-control design ...
Why are case control studies important?
When little is known about the risk factors for the disease, case-control studies provide a way of testing associations with multiple potential risk factors. (This isn't really a unique advantage to case-control studies, however, since cohort studies can also assess multiple exposures.)
Is a case control study retrospective?
Students usually think of case-control studies as being only retrospective, since the investigators enroll subjects who have developed the outcome of interest. However, case-control studies, like cohort studies, can be either retrospective or prospective.
Can you use case control sampling to analyze breast cancer?
There is, however, another more efficient alternative, i.e., to use a case-control sampling strategy. One could analyze all of the blood samples from women who had developed breast cancer, but only a sample of the whole cohort in order to estimate the exposure distribution in the population that produced the cases.
The Nature of Case-Control Studies
Steps Involved in Case-Control Studies
A. Selection of Cases and Controls
- As noted above, it is always useful to think of a case-control study as being nested within some sort of a cohort, i.e., a source population that produced the cases that were identified and enrolled. In view of this there are two key principles that should be followed in selecting controls: 1. The comparison group ("controls") should be representat...
B. Matching
- By definition, a case-control study is always retrospectivebecause it starts with an outcome then traces back to investigate exposures. When the subjects are enrolled in their respective groups, th...
- The case-control study compares the prevalence of suspected causal factors between individuals with disease and controls who do not have the disease. If the prevalence of the fa…
- By definition, a case-control study is always retrospectivebecause it starts with an outcome then traces back to investigate exposures. When the subjects are enrolled in their respective groups, th...
- The case-control study compares the prevalence of suspected causal factors between individuals with disease and controls who do not have the disease. If the prevalence of the factor is significantl...
- Although case-control studies can identify associations, they do not measure risk. An estimate of relative risk, however, can be derived by calculating the odds ratio.
- The case-control method has three distinct features:
C. Measurement of Exposure
- By definition, a case-control study involves two populations – cases and controls.
- The focus is on a disease or some other health problem that has already developed.
- Case-control studies are basically comparison studies. Cases and controls must be comparable with respect to known “confounding factors” such as age, sex, occupation, social status, etc.
- By definition, a case-control study involves two populations – cases and controls.
- The focus is on a disease or some other health problem that has already developed.
- Case-control studies are basically comparison studies. Cases and controls must be comparable with respect to known “confounding factors” such as age, sex, occupation, social status, etc.
- The questions asked relate to personal characteristics and antecedent exposures which may be responsible for the condition studied.
D. Analysis
- The first is to identify a suitable group of cases and a group of controls.
- While the identification of cases is relatively easy, the selection of suitable controls may present difficulties.
- The definition of what constitutes a “case” is crucial to the case-control study.
- It involves two specifications:
Advantages of Case-Control Studies
- The controls may differ from the cases in a number of factors such as age, sex, occupation, social status, etc.
- An important consideration is to ensure comparability between cases and controls. This involves what is known as “matching”.
- Matching is defined as the process by which we select controls in such a way that they are si…
- The controls may differ from the cases in a number of factors such as age, sex, occupation, social status, etc.
- An important consideration is to ensure comparability between cases and controls. This involves what is known as “matching”.
- Matching is defined as the process by which we select controls in such a way that they are similar to cases with regard to certain pertinent selected variables (e.g., age) which are known to influe...
- While matching it should be borne in mind that the suspected aetiological factor or the variable we wish to measure should not be matched, because, by matching, its aetiological role is eliminated...
Limitations of Case-Control Study
- Definitions and criteria about exposure (or variables which may be of aetiological importance) are just as important as those used to define cases and controls.
- Information about exposure should be obtained in precisely the same manner both for cases and controls.
- This may be obtained by interviews, by questionnaires or by studying past records of cases s…
- Definitions and criteria about exposure (or variables which may be of aetiological importance) are just as important as those used to define cases and controls.
- Information about exposure should be obtained in precisely the same manner both for cases and controls.
- This may be obtained by interviews, by questionnaires or by studying past records of cases such as hospital records, employment records, etc.
- It is important to recognize that when case-control studies are being used to test associations, the most important factor to be considered, even more, important than the P. values obtained, is the...
References
- The final step is analysis, to find out: 1. Exposure rates among cases and controls to suspected factor. 2. Estimation of disease risk associated with exposure (Odds ratio).