MHB Conditional Probability vs Normal

[jacobson00]

am a bit confused, if i want to find out for example the P(Having the disease among everyone) , using conditional, would it be total people Having the disease over total population?Prescreening Positive and Have the disease is 66
Prescreening Positive but does not the disease 150
prescreening Negative and Have the disease is 5
prescreening Negative and does not Have the disease is 555 so if using conditional probability, i want to find.P(Having the disease among everyone)

66 +5/ total population (776)

P(Prescreening Positive for everyone)

66+150/776

Am i understanding it correctly?

 

[Jameson]

Hi jacobson00,

Welcome to MHB! :)

I would suggest using parentheses to be more clear, but yes I agree with your approach. There are two ways of having the disease with the way the data is arranged - either you have it and you are prescreened positive or you have it and are prescreened negative. Divide by total number of people. There isn't any overlap between the groups so it seems pretty straightforward and I agree with your answer.

 

[jacobson00]

thank you. I think i was thrown off by the term "Conditional". If looks like plain probabilities.

 

[Jameson]

thank you. I think i was thrown off by the term "Conditional". If looks like plain probabilities.

Well they are conditional probabilities but you are given a lot of information so you don't have to think of them that way.

You could write each of these numbers as a conditional probability and calculate the answer through the law of total probability, but that's not necessary here.

$$P[+|S^{+}], P[+|S^{-}], P[-|S^{+}], P[-|S^{-}]$$

 

[jacobson00]

Phewww! i don't think i am there yet. baby steps. Thank you

 

[Jameson]

Phewww! i don't think i am there yet. baby steps. Thank you

Ha, it looks scarier than it is. :) Glad you found us. Please keep posting your questions so we can help when you are stuck.

 

[jacobson00]

Regression alone enables you to do what? a) infer causality only, b) identify correlation only c) both?