Dear all,
I have a problem with the roctab function.
I have 2 variables : "groupe " : 1 for disease, 0 for no disease
"outcome" wich is a continous variable measuring
PTH, with values from 12 to 58
- roctab groupe outcome, d - gives :
Detailed report of Sensitivity and Specificity
----------------------------------------------------------------------------
--
Correctly
Cut point Sensitivity Specificity Classified LR+
LR-
----------------------------------------------------------------------------
--
( >= 12 ) 0.00% 100.00% 60.00%
1.0000
( >= 14 ) 8.33% 100.00% 63.33%
0.9167
( >= 25 ) 8.33% 94.44% 60.00% 1.5000
0.9706
( >= 29 ) 8.33% 72.22% 46.67% 0.3000
1.2692
( >= 33 ) 8.33% 66.67% 43.33% 0.2500
1.3750
( >= 36 ) 8.33% 61.11% 40.00% 0.2143
1.5000
( >= 38 ) 8.33% 50.00% 33.33% 0.1667
1.8333
( >= 40 ) 8.33% 38.89% 26.67% 0.1364
2.3571
( >= 42 ) 8.33% 33.33% 23.33% 0.1250
2.7500
( >= 44 ) 8.33% 27.78% 20.00% 0.1154
3.3000
( >= 45 ) 16.67% 11.11% 13.33% 0.1875
7.5000
( >= 46 ) 16.67% 0.00% 6.67% 0.1667
( >= 47 ) 25.00% 0.00% 10.00% 0.2500
( >= 48 ) 33.33% 0.00% 13.33% 0.3333
( >= 50 ) 41.67% 0.00% 16.67% 0.4167
( >= 52 ) 50.00% 0.00% 20.00% 0.5000
( >= 53 ) 66.67% 0.00% 26.67% 0.6667
( >= 54 ) 75.00% 0.00% 30.00% 0.7500
( >= 55 ) 83.33% 0.00% 33.33% 0.8333
( >= 58 ) 91.67% 0.00% 36.67% 0.9167
( > 58 ) 100.00% 0.00% 40.00% 1.0000
----------------------------------------------------------------------------
--
How is it possible to have a specificity = 100% and sensitivity = 0% for the
first cut point ? all people >= 12 have to be classifed has "disease people"
because test is abnormal and so sensivity must be 100% and specificity = 0 %
Can someone help me ?!!!
Alvine Bissery
***************************************************************
Alvine BISSERY
Biostatisticienne
H�pital Europ�en Georges Pompidou
Centre d' Investigations Cliniques
20-40, rue Leblanc
75908 PARIS Cedex 15
France
t�l: +33 1 56 09 29 13
fax: +33 1 56 09 29 29
e-mail: [email protected]
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