Sensitivity Specificity

Paraesthesia

97

4

Waking at night

91

14

Anaesthesia

57

61

Phalen's test

58

54

Tinel's test

42

63

Two point discrimination test

6

98

Test positive

lest regative

Condition present

rue pGSibivfi

Ffilse negative

A -r C

Sensitivity A-TC^

Condition absent

F&lse: positive

True negative

E +■ D

Specificity FT +~D

A + Li

Negative :m:LliCtivt: value

LiC -1- D

Sensitivity: How often a test shows pathology tfhen it is present

Specihtity: Now often a test is no-rnal whon no pathology present

Positive predictive value; indicates the Ike ¡hood of the patient nav ng disease irfhei the test s positive

Negative predictive value; indicates the lice iliood of the patient nav ng disease wrhen the test s regative

Fig. 13.1 Definitions of sensitivity, specificity and predictive values

Predictive values that are useful indices of validity can be expressed as positive and negative values. Consider the example of a patient presenting with haematuria. In general practice the positive predictive value for carcinoma as the cause would be less than 5% but about 50% in the inpatient hospital setting.

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