Package dev.nm.stat.descriptive.correlation

Class SpearmanRankCorrelation

  • All Implemented Interfaces:
    Statistic
    public class SpearmanRankCorrelation
extends Object
implements Statistic
    Spearman's rank correlation coefficient or Spearman's rho is a non-parametric measure of statistical dependence between two variables. It assesses how well the relationship between two variables can be described using a monotonic function. If there are no repeated data values, a perfect Spearman correlation of +1 or -1 occurs when each of the variables is a perfect monotone function of the other.

    For a set of observations \((X_i, Y_i)\) we first compute the ranks \(x_i\) and \(y_i\) of the \(X\) and \(Y\) values for each observation. Spearman's rho is defined as the Pearson correlation coefficient between the ranked variables: \[ \rho = \frac{\sum_i(x_i-\bar{x})(y_i-\bar{y})}{\sqrt{\sum_i (x_i-\bar{x})^2 \sum_i(y_i-\bar{y})^2}} \]

    See Also:
    Wikipedia: Spearman's rank correlation coefficient, Covariance.correlation()

    • Constructor Detail

      • SpearmanRankCorrelation

        public SpearmanRankCorrelation​(double[] data1,
                               double[] data2)
        Construct a Spearman rank calculator initialized with two samples. The size of the two sample must be equal.
        Parameters:
        data1 - the first sample
        data2 - the second sample

    • Method Detail

      • addData

        public void addData​(double... data)
        Update the statistic with more data. Since this signature takes only a single array double[], we concatenate the two arrays into one.

        For example, suppose we want to do 

         
 addData(new double[][]{
     {1, 2, 3},
     {4, 5, 6}
 });
        We can also write 
         
 addData(new double[]{
     {1, 2, 3, 4, 5, 6}
 });
        In the latter case, there must be an even number of data points.
        Specified by:
        addData in interface Statistic
        Parameters:
        data - a data array concatenating two samples

      • addData

        public void addData​(double[] data1,
                    double[] data2)
        Add the given two samples. The size of the two samples must be equal.
        Parameters:
        data1 - the first sample
        data2 - the second sample

      • N

        public long N()
        Description copied from interface: Statistic
        Get the size of the sample.
        Specified by:
        N in interface Statistic
        Returns:
        the sample size

      • value

        public double value()
        Description copied from interface: Statistic
        Get the value of the statistic.
        Specified by:
        value in interface Statistic
        Returns:
        the statistic