Please explain

Prep for USMLE Forum

» Log in | Register

Forum

Step 1

Match

Prep4USMLE Forum » USMLE Step 2 CK Forum » Preventive Medicine

Please explain

Author

6 Posts

whiterabbit

07/01/07 - 09:54 PM

55 yr old man with urinary infrequency. PSA of 7. By common standards PSA> 4 is 80% sensitive and 90% specific. In a recent study 10% of men of this age have prostate cancer. What is your estimate of the liklehood that this man has prostate cancer?

a)13%
b)25%c)36%
d)47%
e)58%
f)69%
g)72%
h)81%

Please explain at least in brief..........to see given answer scroll down

..

..........

.........................answer is given as choice D

whiterabbit

07/02/07 - 01:48 PM

Never Mind I figured it out.......

Mahwish Mushtaq
Forum Junior

Topics: 9
Posts: 60

07/03/07 - 11:15 AM

u figured it out but can u explain it plz, i cannot figure out why?

babydoc4usmle
Forum Guru
avatar

Topics: 18
Posts: 634

07/03/07 - 07:28 PM

the question is: what is PPV
so you just have to make 2x2 table
take imaginary population of 1000 peopla and put 10% prevalence (100) in "diseased" total, so 80% sensitivity means that diseased with positive test results are 80 and negative 20
same with specificity (1000-100=900 total healthy)
and last 80/170(total with +ve results) ~ 47%

sandra
Forum Guru

Topics: 199
Posts: 458

11/17/07 - 08:28 AM

are they asking the no. of true positives or the no. of test poitives?

could someone explain using the table. confused

___________________
You become what you think you are!

sandra
Forum Guru

Topics: 199
Posts: 458

11/17/07 - 08:31 AM

ok..now i get it..they are asking for the ppv..

___________________
You become what you think you are!

You don't have permission to post.