Sensitivity and specificity

[Ian Maccie]

Dear Statalister,

Currently, I am working with a simple dataset but I am not sure whether the basic coding is correct. If I run the commands below, will the values listed as sensitivity and specificity be the actual sensitivity and specificity values? Or do I have to interchange the 0 and 1 values in the foreign variable?

Best
Ian


* Dataset

  
webuse auto.dta, clear

* Logistic regression command

  
logit foreign price, vce(cluster make)

. * Logistic regression
. logit foreign price, vce(cluster make)

Iteration 0:   log pseudolikelihood =  -45.03321  
Iteration 1:   log pseudolikelihood = -44.947363  
Iteration 2:   log pseudolikelihood =  -44.94724  
Iteration 3:   log pseudolikelihood =  -44.94724  

Logistic regression                             Number of obs     =         74
                                                Wald chi2(1)      =       0.20
                                                Prob > chi2       =     0.6558
Log pseudolikelihood =  -44.94724               Pseudo R2         =     0.0019

                                  (Std. Err. adjusted for 74 clusters in make)
------------------------------------------------------------------------------
             |               Robust
     foreign |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       price |   .0000353   .0000791     0.45   0.656    -.0001198    .0001904
       _cons |  -1.079792   .5537941    -1.95   0.051    -2.165209    .0056241
------------------------------------------------------------------------------

* Determination of Youdens index

       * Sensitivity and specificity graphs
            lsens , gensens(sens_price) genspec(spec_price)
       * Variable for Youden Index
            gen float youden_price = sens_price + spec_price-1
       * Youden index determination
            egen float max_price = max(youden_price)
       * Cut-off value, sensitivity and specificity
            list sens_price spec_price c.price ///
            if youden_price == max_price

     +-----------------------------+
     | sens_p~e   spec_p~e   price |
     |-----------------------------|
 32. | 0.590909   0.653846   5,379 |
     +-----------------------------+