Difference between revisions of "Documentation/How Tos/Calc: PROB function"

Revision as of 19:21, 1 May 2008

PROB

Returns a result from a list of probabilities.

Syntax:

PROB(values; probabilities; start; end)

values is a range or array of numbers (possibly unordered).

probabilities is a range or array of numbers of the same size as values, indicating the corresponding probability (>0 and <=1) that each value in values will occur. The numbers in probabilities must sum to 1 exactly.

PROB finds all values which are between start and end inclusive and returns the sum of their corresponding probabilities.

end may be omitted, in which case PROB returns the probability corresponding to start (or 0 if start is not present in values).

Advanced topic: PROB evaluates as an array formula - see the examples.

Example:

PROB({3; 4; 5; 6}; {0.2; 0.4; 0.3; 0.1}; 4; 6)

returns 0.8, the sum of the probabilities for 4, 5 and 6.

PROB({2.2; 5; 1}; {0.5; 0.3; 0.2}; 0; 3)

returns 0.7, the sum of the probabilities for 1 and 2.2.

PROB({3; 4; 5; 6}; {0.2; 0.4; 0.3; 0.1}; 4)

returns 0.4, the probability for 4.

Evaluation as an array formula:

PROB(A1:A2*2; B1:B2; 2)

where cells A1, A2 contain 1, 4 and cells B1, B2 contain 0.3, 0.7, returns 0.3. PROB forces evaluation as an array formula, so that A1:A2*2 yields the array {2 | 8}. Thus PROB({2 | 8}; B1:B2; 2) is actually evaluated to give the result.

PROB(A1:A2; B1:B2/100; 4)

where cells A1, A2 contain 1, 4 and cells B1, B2 contain 30, 70, returns 0.7. PROB forces evaluation as an array formula, so that B1:B2/100 yields the array {0.3 | 0.7}. Cells B1 and B2 effectively contain percentages here.

See also:

Statistical functions

Using Arrays