Hi everybody,
I am using Stata to calculate the sensitivity and specificity of a diagnostic test (Amsel score) compared to the golden standard test Nugent score.
The resulting table is
If I use roctab, the results given are:
So, a sensitivity of 95.80% and a specificity of 74.42%. But if I calculate by hand, I get the following results:
True positive: 137
False positive: 6
True negative: 192
False negative: 66
Sensitivity: TP / (TP + FN) = 137 / (137 + 66) = 67.49%
Specificity: TN / (TN + FP) = 192 / (192 + 6) = 96.97%
Positive predictive value: TP / (TP + FP) = 137 / (137 + 6) = 95.80%
Negative predictive value: TN / (TN + FN) = 192 / (192 + 66) = 74.42%
I have the impression I must have made a mistake somewhere, but I cannot find out how and why. Thank you for your help! I am using Stata 13.0.
Kindly, Marijn
I am using Stata to calculate the sensitivity and specificity of a diagnostic test (Amsel score) compared to the golden standard test Nugent score.
Code:
tab BVbyAmsel highnugent, chi2 roctab BVbyAmsel highnugent, detail
Code:
| highnugent
BVbyAmsel | 0 1 | Total
-----------+----------------------+----------
0 | 192 66 | 258
1 | 6 137 | 143
-----------+----------------------+----------
Total | 198 203 | 401
Code:
Correctly Cutpoint Sensitivity Specificity Classified LR+ LR- ------------------------------------------------------------------------------ ( >= 0 ) 100.00% 0.00% 35.66% 1.0000 ( >= 1 ) 95.80% 74.42% 82.04% 3.7451 0.0564 ( > 1 ) 0.00% 100.00% 64.34% 1.0000
True positive: 137
False positive: 6
True negative: 192
False negative: 66
Sensitivity: TP / (TP + FN) = 137 / (137 + 66) = 67.49%
Specificity: TN / (TN + FP) = 192 / (192 + 6) = 96.97%
Positive predictive value: TP / (TP + FP) = 137 / (137 + 6) = 95.80%
Negative predictive value: TN / (TN + FN) = 192 / (192 + 66) = 74.42%
I have the impression I must have made a mistake somewhere, but I cannot find out how and why. Thank you for your help! I am using Stata 13.0.
Kindly, Marijn