Diagnostic Testing

Diagnostic tests are widely used in medicine and many other fields. For electric power infrastructure testing is done on many systems including power transformers and underground cable.

However there is a problem - tests rarely provide perfect predictions. Given this fact, central to diagnostic testing is how to interpret test results.  A rigorous framework for probabilistic interpretation is provided here. The framework is implemented in a computer program.

Click here to download a java app that will allow you to run the Diagnostic Testing software.


Two Key Concepts:

  1. The pre-test probability of the condition is the likelihood of the condition based on your assessment prior to the test.

  2. A test creates two groups - those who test positive and those who test negative -- What is the likelihood that each of these groups has the condition?

The Analytic Framework

Formal probabilistic statements about positive and negative test results require application of Bayes' Theorem and the specification of three parameters. The input parameters are:

  • Your pre-test assessment of the likelihood that an object or group of objects has a specific condition.
  • For the specific test you must specify the probabilities that the test will return a “false positive” and “false negative” result.

With these parameters and Bayes' Theorem you can make formal probabilistic statements about the likelihood that an object has a condition for both positive and negative test outcomes.

Click the Download button to download a java app that will allow you to run a simple diagnostic testing app. Download The Diagnostic Testing App


Instructions For Running the Diagnostic Testing App

NOTE: The Diagnostic Testing app is a Java program (from S.Chapel Associates). The app is designed only for desktop computers. To run the app you must have the java runtime environment (JRE) installed. You can download the latest JRE version from this link: The Java Runtime Environment

  • Enter input parameters or leave the default value.
  • Click the Update Assessment button to compute updated likelihoods of the condition.
  • Click the Explain Results button for an explanation of the updated probabilities.