count2prob | R Documentation |

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).

```
count2prob(x, type = 3)
```

`x` |
input matrix of counts from |

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

Matrix of probabilities per category

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 |

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

`convert2prob`

for conversion of continuous forecasts to ensemble counts

```
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, ]
```

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