Statistics for the Behavioral Sciences, 4/e
Symbols and Formulas
|p(A) ||probability of event A|
|p(A or B) ||probability of event A or event B|
|p(A, B) ||probability of both A and B|
|p(B|A) ||probability of event B given that event A has occurred|
FORMULASFormula 7-1. Equation for the addition rule of probability
p(A or B) = p(A) + p(B)
p(A or B) means the probability of either event A or event B, and it is equal to the probability of event AFormula 7-2. Equation for the multiplication rule of probability
[p(A)] plus the probability of event B [p(B)].
p(A, B) = p(A) x p(B)
p(A, B) is the probability of occurrence of both event A and event B, which is equal to the product of their
individual probabilities. This equation is used when events A and B are independent.Formula 7-3. Equation for determining the probability of a sequence of nonindependent events
p(A, B) = p(A) x p(B|A)
When events A and B are not independent—that is, when the probability of B depends on whether A has
occurred—then the multiplication rule must be modified as shown. p(B|A) reads "probability of B given A."