# Brier Score: assessment of prediction accuracy

### Description

The Brier Score is a probabilistic number of errors that takes the predicted probabilities into consideration. A small Brier Score indicates high prediction accuracy. This function assumes 2-class data, and requires the true class labels to be known.

### Usage

1 | ```
brier.score (predictedArr, truthArr)
``` |

### Arguments

`predictedArr` |
a vector consisting of the predicted probabilities that the test sample belongs to class 1. |

`truthArr` |
a zero-one vector indicating the known class labels of
the test samples. We assume this vector has the same
length as |

### Details

The Brier Score computes the sum of squares of the differences between the true class and the predicted probability over all test samples. If the predicted probabilities are constrained to equal to 0 or 1, the Brier Score is equal to the total number of classification errors.

### Value

A non-negative real number.

### References

Brier, G.W. (1950) Verification of forecasts expressed in terms of probability. Monthly Weather Review 78: 1-3.

Yeung, K.Y., Bumgarner, R.E. and Raftery, A.E. (2005) Bayesian Model Averaging: Development of an improved multi-class, gene selection and classification tool for microarray data. Bioinformatics 21: 2394-2402.

### See Also

`bma.predict`

,
`iterateBMAglm.train.predict`

### Examples

1 2 3 4 5 6 7 8 9 10 11 12 | ```
library (Biobase)
library (BMA)
library (iterativeBMA)
data(trainData)
data(trainClass)
data (testData)
ret.vec <- iterateBMAglm.train.predict (train.expr.set=trainData, test.expr.set=testData, trainClass, p=100)
## compute the Brier Score
data (testClass)
brier.score (ret.vec, testClass)
``` |