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cesine edited this page Apr 13, 2011
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- true positives
- false positives
- true negatives
- false negatives
- actual positives (true positives + false negatives)
- actual negatives (true negatives + false positives)
Medicine is more concerned with high accuracy of the negative test results.
- Sensitivity refers to the probability that a diagnostic technique will detect a particular disease or condition when it does indeed exist in a patient (National Multiple Sclerosis Society). A measure with high sensitivity is sensitive to the existence of the condition, and will avoid false negatives and avoid delayed treatment.
- Specificity refers to the probability that a diagnostic technique will indicate a negative test result when the condition is absent (true negative). A measure with high specificity can be used to eliminate candidate diseases/conditions.
Information retrieval is more concerned with high accuracy of the returned (positive) results.
- Precision (true positives/returned positives) is defined as the number of relevant documents retrieved by a search divided by the total number of documents retrieved by that search. Precision is a measure of correctness, in the context of a final disease diagnosis or final search result few false positives (high precision) is preferred.
- Recall (true positives/actual positives) is defined as the number of relevant documents retrieved by a search divided by the total number of existing relevant documents. Recall is a measure of completeness, in the context of early disease testing or a first pass search, few false negatives (high recall) is preferred.
- F-score is a weighted average of accuracy which simply combines the measures of precision and recall. ( precision * recall) / ( precision + recall)
- apply in conjunction with known tests or tools (to achieve the "actual" values)
- repeated use of the same screening tool with the same client often reduces its validity
- it is advised that some screening tools not be used repeatedly with the same individual if the time interval between testing is short.