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19 Cards in this Set
- Front
- Back
Major problems with measurement
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Information bias.
prospective studies - nondifferential When E is measured after D - diffential |
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Evaluating measurement methods
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biological methods.
subject interview. records. |
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6 Measuring factors
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1)Accuracy and complete
2)Nondifferential 3)Response rate 4)Temporal tracking 5)Availability 6)Cost |
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Current exposure: Biological or physical measurement
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often gold std.
Current: Accuracy and complete ++ nondifferential ++ response rate - temproal tracking + availability + cost - |
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past exposure: biological or physical measurement
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Past
Accuracy and complete -- nondifferential -- response rate -- temproal tracking -- availability -- cost -- |
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Coefficient of variation
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variation expresses as % of the mean
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Interview
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most common method but is problematic for past exposures or exposure after disease
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most common problems of interviews
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poor technique.
fail to cross-check with other data sources. insensitive to counterincentives to accurate reporting |
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Current exposure: Interview
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Current:
Accuracy and complete ? nondifferential + response rate + temproal tracking + availability ++ cost + |
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Past exposure: Interview
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Past
Accuracy and complete - nondifferential - response rate + temproal tracking -- availability + cost + |
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Current exposure: records
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Current:
Accuracy and complete ? nondifferential ++ response rate ++ temproal tracking ++ availability - cost ++ |
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Past exposure: records
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Past:
Accuracy and complete ? nondifferential ++ response rate ++ temporal tracking ++ availability - cost ++ |
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Assessing measurment quality
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Requires gold standard
1)Categorical: Sensitivity, Specificity, PPV 2)Product moment correlation coefficient (Pearson) |
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Indices of reproducibility
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Categorical: Kappa
Continuous: Intra-class correlation |
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Effects of nondifferential measurement error
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Bias towards Null
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Effect of differential exposure misclassification
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Spurious diffences between E+ and E-
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Exposure misclassification in a cohort study
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Baseline measurement.
Unmeasured changes in exposure during followup |
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Exposure misclassification in a case-control study
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1)Recall failure (non-differential)
2)Differential recall between cases and controls |
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Minimizing exposure misclassification
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1)Good technique: Standardized, structureed questions, repeate measures.
2)Use of records 3)Substudy estimate misclassification, mathematical correlation |