# Calculating Posterior Probability with two variables

• Sep 12th 2012, 05:53 AM
rico
Calculating Posterior Probability with two variables
Hey Guys,

Calculate the posterior probability of patient having flu given cough positive and fever negative?

Sensitivity of cough for flu: 60%
Sensitivity of fever for flu: 70%
Specificity of fever for flu: 80%
Specificity of cough for flu: 50%
Prior of flu: 10%

Greatly appreciated!
(Happy)

Rico
• Sep 12th 2012, 11:15 AM
MaxJasper
Re: Calculating Posterior Probability with two variables
Quote:

Originally Posted by rico
Calculate the posterior probability of patient having flu given cough positive and fever negative?
Sensitivity of cough for flu: 60%
Sensitivity of fever for flu: 70%
Specificity of fever for flu: 80%
Specificity of cough for flu: 50%
Prior of flu: 10%
Greatly appreciated!
(Happy)Rico

$P({flu})=.10$

$P({cough}|{no\_fever})=\frac{.60+.80}{.60+.70+.8 0+.50}=.53846$

$P({cough}|{flu})=p({flu})*P({cough}|{no\_fever})=. 053846$

double check this!
• Sep 15th 2012, 01:51 PM
rico
Re: Calculating Posterior Probability with two variables
Thanks!!