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PHC 6000: CaCo
Introduction to epidemiology: Case-control studies
| Question | Answer |
|---|---|
| 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
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