// Second line of the table on page 379 of Ayala. The three parameter model matches two parameter model when chi = 0
public void GetInformation_SecondValueLineFromAyala_ReturnsCorrectInfo()
{
ThreeParamModelParameters modelParameters = new ThreeParamModelParameters(2.954, .560, 0);
ThreeParamItemInformationFunction informationFunction = new ThreeParamItemInformationFunction(modelParameters);
const double theta = .3;
var calculatedInformation = informationFunction.GetInformation(theta);
const double expectedInfo = 1.889;
Assert.AreEqual(expectedInfo, calculatedInformation, Tolerance);
}
public void GetInformation_NonzeroChi_ReturnsCorrectInfo()
{
double alpha = 2;
double chi = .5;
double delta = 1;
ThreeParamModelParameters modelParameters = new ThreeParamModelParameters(alpha, delta, chi);
ThreeParamItemInformationFunction informationFunction = new ThreeParamItemInformationFunction(modelParameters);
const double theta = .3;
ThreeParamProbabilityFunction probabilityFunction = new ThreeParamProbabilityFunction(new ThreeParamModelParameters(alpha, delta, chi));
double p = probabilityFunction.ProbabilityOfCorrectResponse(theta);
double expectedInfo = alpha * alpha * Math.Pow((p - chi) / (1 - chi), 2) * ((1 - p) / p);
var calculatedInformation = informationFunction.GetInformation(theta);
Assert.AreEqual(expectedInfo, calculatedInformation, Tolerance);
}
