Re: 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 statemenst
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?

1) What percantage of obesity in the general
population is
attributable to the effect of the virus.

2) What is the likelyhood that you will become obese
if you contract
the virus.




We are given

P(virus) = .20
P(virus|obesity) = .40
P(obesity) = .30

The conditional probability for the second question is, from Bayes formula,

P(obesity|virus) = P(virus|obesity)*P(obesity)/P(virus) = (.40)*(.30)/.20 = .12/.20 = .60.

Jack
.

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