Re: Is this enough information to make an inference?

On Dec 29, 6:55 am, "Luis A. Afonso" <lic...@xxxxxxxxxxx> wrote:
MichaelMichalchik

__________p(obese|virus) = 0.40
__________p(obese) = 0.30
__________p(virus) = 0.20

1) p(obese|virus) = p(obese and virus) / p(virus)

2) p(obese)*p(virus)
(these two features are INDEPENDENT as you say at 1).

Luis Amaral Afonso

*** Date: Dec 28, 2007 4:09 PM
Author: MichaelMichalchik
Subject: Is this enough information to make an inference?

A link has been discovered between a certain virus (adeno-virus 36) and obesity. Casual mechanisms are being elucidated biochemically but I was wondering if there are any general statement we can make about the virus's contribution to the obesity epidemic.
 Given:

 1) The virus is a causal risk factor for obesity and that obesity is not a risk factor for catching the virus.
 2) 20% of the general population tests positive for the virus.
 3) 40% of obese people test positive for the virus.
 4) 30% of the united  states is obese.

 Can we infer?
A) What percantage of obesity in the general population is
attributable to the effect of the virus.
B) What is the likelyhood that you will become obese if you contract the virus.***

I am sorry but I don't think I am understanding the notation you are
using. What is the difference between "p(obese|virus)" and "p(obese
and virus)".

Also your second formula seems to lead to an impossible conclusion.

2) p(obese)*p(virus)

which is .3 x .2 = .06 which would seem to indicate that your chances
of being obese after catching the virus would be 6%(way below the
general population). BTW the probabilities are not independent,
obesity depends to some extent on the presence of virus, but for sake
of this problem at least, we assume that obesity does not effect the
probability of catching the virus.

.

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