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22 Cards in this Set
- Front
- Back
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In cases of observations when can a conclusion be made
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Only when comparative observations are present in noncases. Comparison is an essential component of epi investigation and shown in case-control study design
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WHAT IS DESIGN OF CASE CONTROL STUDIES
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CASES CONTROLS
HAVE DZ DO NOT HAVE DZ EXP NOT EXP EXP NOTXP |
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Describe a/a+c and b/b+d and ratio proportions and their meaning
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a and c are cases with disease - a exposed, c, not exposed. b, controls exposed and d, controls not exposed, without disease. a + c are total cases and b + d are total controls. a/a+c and b/b+d are proportions exposed. One would expect proportions a/a+c (cases exposed) to be greater than b/b+d (controls exposed) if association.
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Does the ratio of cases to controls represent the prevalence of the disease in the population?
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No, this was determined by the investigator and clearly does NOT represent prevalence.
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What is the hallmark of case control studies?
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Starts with cases and compares them to those without disease (controls)
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How is the design of case control study compared to cohort study
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case-control starts by comparing people with disease(cases) wthout disease(controls). in contrast to design of cohort, which begins with exposed and compares to nonexposed groups.
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Is it true that case-control studies go backward in time and cohorts go forward in time?
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NO< wrong! Mistakenly thought because retrospective is used for case-control. Time is not the characteristic that distinguishes the two designs.
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What distinguishes case-control studies from cohort studies?
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whether the study begins with disease vs non-disease (case-control) or with exposed and nonexposed(cohort)
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What does dichotomized mean
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exposed or nonexposed
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is it preferable to use incident cases or prevalence cases in case-control studies?
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incident is generally preferable.
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Why is incidence case better to use for case control than prevalence?
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risk factors in prevalence cases will be related more to survival than to development of disease.
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What is most difficult problem in selection in case control studies?
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selecting the controls
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WHAT IS GROUP MATCHING IN CONTROLS
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also called frequency matching, consists of selecting controls so proportion of controls with certain characteristic is identical to proportion of cases with same characteristic.
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example of group matching:
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if 25% of cases are married, select 25% controls also married. select cases FIRST
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WHAT IS INDIVIDUAL MATCHING
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or 'matched pairs' for each case selected, a control is selected who is similar to the case in terms of specific variables of concern. (age, race, etc)
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where is individual case control matching often seen
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hospital cases. a case is selected and the next patient who 'matches'' to enter hospital is tagged for control.
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what are two major problems with matching
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PRACTICAL AND CONCEPTUAL
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describe practical problems with matching controls
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depending on the number of variables trying to match, can be hard to find a control (ie age, race, sex, same zip code, etc). Can get too specific
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what is conceptual problem with matching cases and controls?
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once case is matched to control according to a given characteristic, cannot study that characteristic. cases and controls will be identical in regard to that characteristic
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what do you not want to match on when selecting controls for cases?
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Anything you might want to study.
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what is used to match in case-control studies?
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only match variables that are considered risk factors for the disease.
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what is overmatching
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matching on variables other than risk factors
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