Expert: Sherry Wallin - 2/18/2011

Question
after examining a collection of newspaper articles about politics, following joint probabilities have been
estimated :
__________________________________________________________
         economy                         ~economy
     crisis  ~crisis                crisis  ~crisis
oil   0.576     0144                  0.064    0.016
~oil  0.008     0.072                 0.012    0.108
__________________________________________________________
Where w denotes the presence and ~w the absence of word w. Compute the following:
a) p(economy).
b) p(oil) and p(~oil).
c) p(economy | oil) and p(~economy | oil).
d) p(oil | economy; crisis) and p(~oil | economy; crisis).

Answer
Neelufar~

a) The probability of having economy is just the sum of the probabilities under economy  whether in crisis or not or with oil or not. [By the way, you missed putting the decimal point for 0.144]

b) The probability of oil and not oil is the empty set therefore 0, because it is impossible to have both occur at the same time.

c)  The probability of economy given oil and not economy given oil is again the empty set. You can't have economy and not economy at the same time regardless if you have oil or not.

d)  I am not sure what you mean by using the notation P(A|B;C) so I can't address this question, sorry.


Math Prof