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PHC 6000: CaCo

Introduction to epidemiology: Case-control studies

For selection of cases, what must be established first? Clear diagnostic criteria and a well defined source population of cases
Comment on the sensitivity and specificity of diagnostic criteria for selection of cases Should be sensitive enough to minimize the likelihood that an affected person is missed, but at the same time be specific enough to minimize non-affected persons being misclassified as cases
What is the disadvantage to using restrictive criteria for the selection of cases? May require information that is not available for all cases
Cases should be representative of all cases in the population. (T/F) True
Is there a preference for incident vs. prevalent cases? Why? Incident cases are preferable cases to reduce recall bias and over-representation of cases of long duration
Why is it important to minimize over-representation of cases of long duration? Exposure could be a prognostic factor, or diagnostic criteria can change
When dealing with a strong prognostic factor, which type of cases are preferred? Incident cases
What are prognostic factors? Factors that affect survival
Is it ok to ever use prevalent cases in a case-controls tudy? In modern times using prevalent cases is NOT ok
The likelihood of cases being included in the stud should be related to their study status. (T/F) False; it must NOT BE related to their study status
Is the search for exposure retrospective or prospective in case-control studies? Retrospective
Evidence from a case-control study may be so compelling that a potentially expensive cohort study becomes unnecessary. (T/F) True
What are the main steps to a case-controls study? At baseline select cases & controls based on disease status; exposure status is unknown. Exposure is determined retrospectively in cases and controls; multiple exposures can be assessed. Results analyzed based on diff in exposure btwn cases & controls.
What sources can be used to identify cases? Surveillance systems, hospital and medical records, mortality records
A good way to obtain cases is to include all incident cases in a defined population over a specified period of time. (T/F) True
What are population-based cases? All subjects or a random sample of all subjects with the disease at a single point or during a given period of time in the defined source population
What are hospital-based cases? All patients with the diagnosis of interest in a hospital department at a given time
What is the relationship between study inclusion and exposure status of cases? The likelihood of cases being included in the study must not be related to their exposure status
What is the relationship between participation and exposure status of controls? Participation does not depend on exposure; sample of controls should have the same prevalence of exposure as the source population, or as cases if there was no relation between exposure and disease
What is the purpose of a control group? To provide an estimate of the exposure rate that would be expected to occur in the cases if there were no association between the study disease and exposure
What population should controls come from? The same population at risk for the disease as the cases, and representative of the source population
What is comparable-accuracy? Allows for equal reliability in the information obtained from cases and controls. Information is collected identically regardless of disease status.
What are the advantages of using general population controls? -Source population is better defined -Less prone to selection bias
What are the disadvantages of using general population controls? -Costly and time consuming -Perhaps more prone to recall bias -Eventually high non-response rate
What are the advantages of using hospital controls? -Easy to ID participants, better access to them, better cooperation -More ability to verify exposure in medical records or specimens -Less recall bias -Higher response rate -SES can be balanced between cases and controls
What are the disadvantages of using hospital controls? -Referral patterns can render source population less defined (differential referral for different diagnoses) -Possibility of controls' condition being related to exposure of interest
Should the number of concurrent conditions matter when selecting hospital-based controls? Avoid patients who have multiple concurrent conditions
How can we minimize risk factors from being over-represented among hospital-based controls? Select controls from various diagnostic groups
How can we minimize the condition from being influenced by exposures among hospital-based controls? Select controls from patients with acute conditions
When selecting hospital-based controls, select patients with diagnoses known to be related to the risk factor of interest. (T/F) False; DO NOT do this!
If all cases are diagnosed in the community, what is a suitable source of controls? Sample of general population
If all cases are diagnosed in a sample of the population, what is a suitable source of controls? Non-cases in a sample of the population
If all cases are diagnosed in all hospitals, what is a suitable source of controls? Sample of patients in all hospitals who do not have the disease
If all cases are diagnosed in a single hospital, what is a suitable source of controls? Sample of patients in the same hospital who do not have the disease
If cases are diagnosed either in the community, are a sample of the population, or in a hospital, what are other suitable sources of controls? Spouses, siblings, or associates of cases
Questionnaires and interviews are prone to what type of bias? Recall and interviewer bias
What is the disadvantage to using a biological assessment of exposure? -The exposure of interest may not have a suitable biomarker -The biomarker may be transient -Obtaining specimens can be invasive (deter participation) -The disease can alter the biomarker's metabolism, distorting case-control comparisons
What is the disadvantage to using medical, occupational, or other records for assessment of exposure? These can be limited and not standardized
What type of cases are used to avoid modification of risk behavior after diagnosis? Prevalent cases
What are nested case-control studies? Case-controls studies done within an ongoing cohort study
Why would someone want to conduct a nested case-control study? In large cohorts, it is often more efficient to construct a case-control study within the cohort, once a significant number of cases have emerged, to study a specific exposure not measured at baseline (new hypothesis)
How is it possible to measure the exposure retroactively in a cohort study? -A specimen had been stored but not analyzed -An interview is conducted to ask about an exposure not assessed at baseline -Records of exposure are retrieved that were not thought about when the cohort was first assembled
What are the advantages of nested case-control studies? -Recall bias eliminated since data on exposure obtained b4 disease develops -Exposure data more likely to represent pre-illness since obtained b4 clinical illness diagnosed -Costs reduced; lab tests need to be done only on specimens from select subjects
What happens to the OR when controls have high degrees of exposure? Biased toward the null; artificially low
What happens to the OR when controls have low degrees of exposure? Biased away from the null; artificially high
If cases are chronic disease patients, what is a suitable source of controls? Accident/injury patients
What is a problem for using accident/injury patients as controls for chronic disease patients? How can this be resolved? Differences in age; solution would be to match on age
For extremely rare diseases, how can power be increased without having to find more cases? Increase number of matched controls
Is risk ever measured in a case-control study? No, only odds!
Can matched variables be evaluated as risk factors? No
Created by: AlneciaPHS