Sensitivity & specificity explained, including positive predictive value & negative predictive value

In this epidemiology tutorial you will learn how to calculate sensitivity and specificity of a diagnostic test. I will also cover positive predictive value (PPV) and negative predictive value (NPV), and the role of prevalence in this context.

About me:
I am a registered clinical epidemiologist and working as a fellow in medical oncology in the Netherlands. I have published over 50 manuscripts and have received several large research grants. I am particularly interested in research in geriatric oncology and am a an active member of the International Society for Geriatric Oncology.

You can find more information about my work on my linkedin page:

And here is my full bibliography:

Disclaimer:
Views and opinions are my own. Examples from clinical research will always include either my own work, or previously published research. I will include references in the description box.

[abrahaleytewele]

hello, it is an amazing tutorial, but you have exchanged the formula of sensitivity with Positive predictive value (PPV) and implies specificity also.

[francescopisu]

2.53 "Even if the test has not a very good specificity, so is able to classify the patients without the disease".
I'm having a hard time trying to understand that bit. If my understanding is correct, a test which has low specificity wouldn't be able to classify patients without the condition. Am I wrong ?

[hassanwaqar]

a beautiful girl and a an excellent lecture

[sbyjutr]

Your box plot is not correct, you are supposed to have Disease/No Disease (reality) on top, and the test to the left. You have it opposite... your math is still right, but this isnt how industry writes out the box plot... because if we use NPV/PPV/Sens/Spec equations on this box plot you have, we would get different answers