Apple iWork '09 - Manual (Page 283)

Chapter 10 Statistical Functions 283
 probability-values: The collection containing the probability values. probability-
values is a collection containing number values. The sum of the probabilities must
add up to 1. Any string values are ignored.
 lower: The lower limit or bound. lower is a number value.
 upper: An optional upper limit or bound. upper is a number value and must be
greater than or equal to lower.
Usage Notes
The PROB function sums the probabilities associated with all values in the collection Â
greater than or equal to the specified lower limit value and less than or equal to the
specified upper limit value. If upper is omitted, PROB returns the probability of the
single number equal to the specified lower limit.
The two arrays must be of the same size. If text is contained in an array, it will be
Â
ignored.
Examples
Assume you are thinking of a number from 1 to 10 to have someone guess. Most people would say
the probability that you would be thinking of a particular number is 0.1 (10%), as listed in column
C, since there are ten possible choices. However, studies have shown that people do not choose
numbers randomly.
Assume that a study has shown that people like you are more likely to select certain numbers than
others. These revised probabilities are in column E.
=PROB(A1:A10, C1:C10, 4, 6) returns 0.30, the probability that the value is 4, 5, or 6, assuming choices
are completely random.
=PROB(A1:A10, E1:E10, 7) returns 0.28, the probability that the value is 4, 5, or 6, based on the research
that numbers are not chosen randomly.
=PROB(A1:A10, E1:E10, 4, 6) returns 0.20, the probability that the value is 7, based on the research that
numbers are not chosen randomly.
=PROB(A1:A10, C1:C10, 6, 10) returns 0.50, the probability that the value is greater than 5 (6 to 10),
assuming choices are completely random.