easyVerification (version 0.4.5)

count2prob: Convert Ensemble Counts to Probabilities

Description

Using plotting positions as described in Wilks (2011), counts of occurrences per forecast category are converted to probabilities of occurrence. For ensembles of size 1 (e.g. verifying observations), the count vector is returned unaltered (corresponding to occurrence probabilities of 0 or 1).

Usage

count2prob(x, type = 3)

Value

Matrix of probabilities per category

Arguments

x

input matrix of counts from convert2prob

type

selection of plotting positions (default to 3, see Types)

Types

The types characterize the plotting positions as specified in Wilks (2011). The plotting positions are computed using the following relationship:

$$p(x_i) = \frac{i + 1 - a}{n + 1 - a}$$

where i is the number of ensemble members not exceeding x, and n is the number of ensemble members. The types are characterized as follows:

type	description	a
1	Weibull	0
2	Bernard and Bos-Levenbach	0.3
3	Tukey	1/3
4	Gumbel	1
5	Hazen	1/2
6	Cunnane	2/5

References

Wilks, D.S. (2011). Statistical methods in the atmospheric sciences (Third Edition). Academic press.

See Also

convert2prob for conversion of continuous forecasts to ensemble counts

Examples

tm <- toymodel()

## convert to tercile forecasts (only display first forecast and obs)
count2prob(convert2prob(tm$fcst, prob = 1:2 / 3))[1, ]
count2prob(convert2prob(tm$obs, prob = 1:2 / 3))[1, ]