Date: Wed, 16 Dec 1998 19:55:27 -0500
Reply-To: "Dr. Mingwei Li" <Mingwei@SURGMON.COM>
Sender: "SPSSX(r) Discussion" <SPSSX-L@UGA.CC.UGA.EDU>
From: "Dr. Mingwei Li" <Mingwei@SURGMON.COM>
Subject: Re: Sensitivity and specificity
how to unsubscribe spssx-l?
From: Hassane ABIDI <hassanab@LYON-SUD.UNIV-LYON1.FR>
To: SPSSX-L@UGA.CC.UGA.EDU <SPSSX-L@UGA.CC.UGA.EDU>
Date: Wednesday, December 16, 1998 3:23 AM
Subject: Sensitivity and specificity
Here is my problem:
n1= all patients where the diagnostic test was positive was selected,
n2= patients randomly selected from the population where the diagnostic test was negative,
According to the real status to the disease we obtain the fourfold table:
| Yes | No
T+ | a | b | n1 (all cases)
T- | c | d | n2
May I estimate the sensitivity by a/(a+c) and specificity by d/(b+d) ?
Or I must take account the prevalence of disease (p) in general population, the positive and negative predictive values (estimated by a/n1 and d/n2 respectively) ?
I have the formulae of the predictive values as function of the prevalence, sensitivity and specificity (Fleiss J.L., 1981 from page 4).
May I use the inverse of these formulae to estimate sensitivity and specificity ?
Any suggestions are welcome,