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Diagnostic test

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Allows to calculate test characteristics such as sensitivity, specificity, positive and negative likelihood ratio, disease prevalence as well as positive and negative predictive value, from data entered in a 2x2 table.

Required input

Enter the number of cases in the diseased group that test positive and negative (left column); and the number of cases in the non-diseased group that test positive and negative (right column).

Note: you can change the order of columns and rows by clicking the Transpose button.

Dialog box for diagnostic test

Disease prevalence

If the sample sizes in the positive (Disease present) and the negative (Disease absent) groups do not reflect the real prevalence of the disease, you can enter the disease prevalence in the corresponding input box. This will have an effect on the positive and negative predictive values, and accuracy.

Dialog box for diagnostic test


The following statistics are reported with their 95% Confidence intervals:

Sensitivity, specificity, disease prevalence, positive and negative predictive value as well as accuracy are expressed as percentages.

Confidence intervals for sensitivity, specificity and accuracy are "exact" Clopper-Pearson confidence intervals.

Confidence intervals for the likelihood ratios are calculated using the "Log method" as given on page 109 of Altman et al. 2000.

Confidence intervals for the predictive values are the standard logit confidence intervals given by Mercaldo et al. 2007; except when the predicitive value is 0 or 100%, in which case a Clopper-Pearson confidence interval is reported.

In the Comment input field you can enter a comment or conclusion that will be included on the printed report.


See also

Recommended book

Book cover

Statistics with Confidence: Confidence Intervals and Statistical Guidelines
Altman DG, Machin D, Bryant TN, Gardner MJ (Eds)

Buy from Amazon

This introduction to confidence intervals has been updated and expanded to include methods for using confidence intervals, with illustrative worked examples and extensive guidelines and checklists to help the novice. There are six new chapters on areas such as diagnostic studies and meta-analyses.