com.itemanalysis.psychometrics.reliability.KR21.java Source code

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Here is the source code for com.itemanalysis.psychometrics.reliability.KR21.java

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/*
 * Copyright 2012 J. Patrick Meyer
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.itemanalysis.psychometrics.reliability;

import com.itemanalysis.psychometrics.data.VariableAttributes;
import org.apache.commons.math3.distribution.FDistribution;

import java.util.ArrayList;
import java.util.Formatter;

/**
 *
 * @author J. Patrick Meyer <meyerjp at itemanalysis.com>
 */
public class KR21 extends AbstractScoreReliability {

    private double mean = 0.0;

    private double sd = 0.0;

    public KR21(int numberOfItems, double testMean, double testStdDev, boolean unbiased) {
        nItems = numberOfItems;
        mean = testMean;
        sd = testStdDev;
        this.unbiased = unbiased;
    }

    public KR21(int numberOfItems, double testMean, double testStdDev) {
        this(numberOfItems, testMean, testStdDev, false);
    }

    public ScoreReliabilityType getType() {
        return ScoreReliabilityType.KR21;
    }

    public double value() {
        double nI = (double) nItems;
        double c = nItems / (nItems - 1.0);
        double kr21 = c * (1.0 - (mean * (nI - mean)) / (nI * sd * sd));
        return kr21;
    }

    @Override
    public double[] itemDeletedReliability() {
        double[] delRel = new double[1];
        delRel[0] = value();
        return delRel;
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        Formatter f = new Formatter(builder);
        String f2 = "%.4f";
        f.format("%7s", "KR-21: ");
        f.format(f2, this.value());
        return f.toString();
    }

    public String ifDeletedToString(ArrayList<VariableAttributes> var) {
        return "";
    }

}