/**
* Correlation when one variable (X) is binary: r = (bar(x1) - bar(x0)) * sqrt(p(1-p)) / sx ,
* where bar(x1) = mean of X when Y is 1 bar(x0) = mean of X when Y is 0 sx = standard deviation
* of X p = proportion of values where Y=1
*/
public double pointBiserialCorrelation() {
// here, Y = {incorrect = 0,correct = 1}, X = confidence
double x0bar = getAverageIncorrectConfidence();
double x1bar = getAverageCorrectConfidence();
double p = (double) this.numCorrect / size();
double sx = getConfidenceStandardDeviation();
return (x1bar - x0bar) * Math.sqrt(p * (1 - p)) / sx;
}
/** Standard deviation of confidence scores */
public double getConfidenceStandardDeviation() {
double mean = getConfidenceMean();
double sumSquaredDifference = 0.0;
for (int i = 0; i < size(); i++) {
double conf = ((EntityConfidence) confidences.get(i)).confidence();
sumSquaredDifference += ((conf - mean) * (conf - mean));
}
return Math.sqrt(sumSquaredDifference / (double) size());
}
/**
* Calculate pearson's R for the corellation between confidence and correct, where 1 = correct and
* -1 = incorrect
*/
public double correlation() {
double xSum = 0;
double xSumOfSquares = 0;
double ySum = 0;
double ySumOfSquares = 0;
double xySum = 0; // product of x and y
for (int i = 0; i < size(); i++) {
double value = ((EntityConfidence) confidences.get(i)).correct() ? 1.0 : -1.0;
xSum += value;
xSumOfSquares += (value * value);
double conf = ((EntityConfidence) confidences.get(i)).confidence();
ySum += conf;
ySumOfSquares += (conf * conf);
xySum += value * conf;
}
double xVariance = xSumOfSquares - (xSum * xSum / size());
double yVariance = ySumOfSquares - (ySum * ySum / size());
double crossVariance = xySum - (xSum * ySum / size());
return crossVariance / Math.sqrt(xVariance * yVariance);
}