modelEval | R Documentation |
Using predictions of given model produced by predict.CoreModel
and correct labels,
computes some statistics evaluating the quality of the model.
modelEval(model=NULL, correctClass, predictedClass, predictedProb=NULL, costMatrix=NULL, priorClProb = NULL, avgTrainPrediction = NULL, beta = 1)
model |
The model structure as returned by |
correctClass |
A vector of correct class labels for classification problem and function values for regression problem. |
predictedClass |
A vector of predicted class labels for classification problem and function values for regression problem. |
predictedProb |
An optional matrix of predicted class probabilities for classification. |
costMatrix |
Optional cost matrix can provide nonuniform costs for classification problems. |
priorClProb |
If |
avgTrainPrediction |
If |
beta |
For two class problems |
The function uses the model
structure as returned by CoreModel
,
predictedClass
and predictedProb
returned by
predict.CoreModel
. Predicted values are compared with true values
and some statistics are computed measuring the quality of predictions.
In classification only one of the predictedClass
and predictedProb
can be NULL
(one of them is computed from the other under assumption that class label is assigned to the most probable class).
Some of the returned statistics are defined only for two class problems, for which the
confusion matrix specifying the number of instances of true/predicted class is
defined as follows,
true/predicted class | positive | negative |
positive | true positive (TP) | false negative (FN) |
negative | false positive (FP) | true negative (TN) |
Optional cost matrix can provide nonuniform costs for classification problems. For regression
problem this parameter is ignored. The costs can be different from the ones used for building the model
in CoreModel
and prediction with the model in predict.CoreModel
.
If no costs are supplied, uniform costs are assumed.
The format of the matrix is costMatrix(true_class, predicted_class)
.
By default a uniform costs are assumed, i.e., costMatrix(i, i) = 0
, and costMatrix(i, j) = 1
,
for i
not equal to j
. See the example below.
If a non-CORElearn model is evaluated, one should set model=NULL
, and a vector of prior of class
probabilities priorClProb
shall be provided in case of classification,
and in case of regression avgTrainPrediction
shall be the mean of prediction values
(estimated on a e.g., training set).
For classification problem function returns list with the components
accuracy |
classification accuracy, for two class problems this would equal accuracy= (TP+TN) / (TP+FN+FP+TN) |
averageCost |
average classification cost |
informationScore |
information score statistics measuring information contents in the predicted probabilities |
AUC |
Area under the ROC curve |
predictionMatrix |
matrix of miss-classifications also confusion matrix |
sensitivity |
sensitivity for two class problems (also called accuracy of the positive class, i.e., acc+, or true positive rate), sensitivity=TP/(TP+FN) |
specificity |
specificity for two class problems (also called accuracy of the negative class, i.e., acc-, or true negative rate), specificity=TN/(TN+FP) |
brierScore |
Brier score of predicted probabilities (the original Brier's definition which scores all the classes not only the correct one) |
kappa |
Cohen's kappa statistics measuring randomness of the predictions; for perfect predictions kappa=1, for completely random predictions kappa=0 |
precision |
precision for two class problems precision=TP/(TP+FP) |
recall |
recall for two class problems (the same as sensitivity) |
F-measure |
F-measure giving a weighted score of precision and recall for two class problems F = (1+beta^2)*recall*precision / (beta^2 * recall + precision) |
G-mean |
geometric mean of positive and negative accuracy, G=sqrt(sensitivity * specificity) |
KS |
Kolmogorov-Smirnov statistics defined for binary classification problems, reports the distance between the probability distributions of positive class for positive and negative instances, see (Hand, 2005), value 0 means no separation, and value 1 means perfect separation, KS = max_t |TPR(t)-FPR(t)|, see definitions of TPR and FPR below |
TPR |
true positive rate TPR = TP / (TP+FN) at maximal value of |
FPR |
false positive rate FPR = FP / (FP+TN) at maximal value of |
For regression problem the returned list has components
MSE |
square root of Mean Squared Error |
RMSE |
Relative Mean Squared Error |
MAE |
Mean Absolute Error |
RMAE |
Relative Mean Absolute Error |
Marko Robnik-Sikonja
Igor Kononenko, Matjaz Kukar: Machine Learning and Data Mining: Introduction to Principles and Algorithms. Horwood, 2007
David J.Hand: Good practice in retail credit scorecard assesment. Journal of Operational Research Society, 56:1109-1117, 2005)
CORElearn
,
CoreModel
,
predict.CoreModel
.
# use iris data # build random forests model with certain parameters model <- CoreModel(Species ~ ., iris, model="rf", selectionEstimator="MDL",minNodeWeightRF=5, rfNoTrees=100, maxThreads=1) # prediction with node distribution pred <- predict(model, iris, rfPredictClass=FALSE) # Model evaluation mEval <- modelEval(model, iris[["Species"]], pred$class, pred$prob) print(mEval) # use nonuniform cost matrix noClasses <- length(levels(iris[["Species"]])) costMatrix <- 1 - diag(noClasses) costMatrix[3,1] <- costMatrix[3,2] <- 5 # assume class 3 is more valuable mEvalCost <- modelEval(model, iris[["Species"]], pred$class, pred$prob, costMatrix=costMatrix) print(mEvalCost) destroyModels(model) # clean up
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