Note: This page now accepts data where either a comma (,) or point (.) is used as the decimal separator.
This utility calculates test sensitivity and specificity for a test
producing a continuous outcome. Suggested cut-points are calculated for a
range of target values for sensitivity and specificity. A ROC curve and two-grah
ROC curve are generated and Youden's index (J
and test efficiency (for selected prevalence values (are also calculated).
Inputs are the desired level of confidence in the resulting sensitivity and specificity
estimates and two columns of data for analysis.
Data required is a series of test results for both infected and uninfected
individuals. This data can be pasted in either of two formats:
- Stacked - the first column contains status identifiers as either "Infected"
or "Uninfected" and the second column contains the corresponding test result; or
- Unstacked - separate columns contain test results for infected and uninfected individuals.
Column order is unimportant but columns must be labelled appropriately as "Infected"
or "Uninfected" in a header row.
Regardless of the format used, the first row must contain column headers.
Additional columns of data will be ignored.
- numerical and graphical summaries of testing results for both infected and uninfected groups;
- cut-point values to achieve minimum target vaues for both sensitivity and
specificity along with corresponding estimates and Wilson binomial confidence intervals;
- one- and two-graph ROC curves, with estimated AUC for the one-graph curve;
- Area under the ROC curve (AUC) and associated DeLong confidence limits and Z test.
See DeLong et al. (1988). Comparing the areas under two or more correlated receiver operating
characteristic curves: a nonparametric approach. Biometrics 44:837-845;
- graphs of Youden's J Index and test efficiency for a range of prevalence values;
- graphs of mis-classification cost terms for a range of prevalence values
and relative costs of false negative/false positive; and
- detailed sensitivity and specificity results in a downloadable spreadsheet file.
For more information, see Greiner, M, Pfeiffer, D and Smith, RD (2000). Principles and practical application of
the receiver-operating characteristic analysis for diagmostic tests. Preventive
Veterinary Medicine 45:23-41.