Calculate the probability of an outcome based on clinical conditions and diagnostic tests
With Bayes' Theorem, the pretest probability is likelihood of an event or outcome based on demographic, prognostic, and clinical factors prior to diagnostic testing. In order to calculate the post-test probability, one must know the likelihood of having either a positive or negative test result in the current clinical situation. The likelihood ratio of a positive diagnostic finding is calculated with the following formula.
In other diagnostic instances with Bayes' Theorem, negative test results are the focus of the diagnostic study or treatment regimen. The likelihood ratio of a negative diagnostic test result can be found with the following formula.
Most diagnostic tests provide an outcome that is dichotomous for "positive" or "negative" for a given disease state or outcome/event. However, if the diagnostic test uses a continuous scale to produce diagnostic results, then researchers can generate the positive likelihood ratio for each different cut-off along the numerical continuum. There are three steps to calculating these likelihood ratios according to Bayes' Theorem:
1. Convert the pretest probability to pretest odds with the first formula below.
2. Multiply the pretest odds by the likelihood ratio to get the post-test odds (second formula below).
3. Convert the post-test odds back into a probability with the third formula below.
Statistician Services for Professionals
Eric Heidel, Ph.D. will provide the following services for researchers, professionals, and organizations at $100/hour. Secure checkout is available with Stripe or PayPal.
- Statistical Analysis
- Research Design
- Sample Size Calculations
- Diagnostic Testing and Epidemiological Calculations
- Survey Design and Psychometrics
AppNotch: Convert this website into an Android and iOS app.
AppNotch team will notify you when your app gets approved in Google Play and Apple iTunes App Stores. Once your app goes live, enter your App Store URLs in this property window, publish your Weebly site and your app store icons will be visible in this page.
Please visit AppNotch.com FAQ to learn more about how to add App Store icons to your website, update your app, send Push notifications and more.
Professional Statistician For Hire!
Copyright © 2017 Scalë. All Rights Reserved. Patent Pending.