Package org.hipparchus.stat.inference

Class TTest

java.lang.Object
org.hipparchus.stat.inference.TTest
public class TTest extends Object
An implementation for Student's t-tests.

Tests can be:

  • One-sample or two-sample
  • One-sided or two-sided
  • Paired or unpaired (for two-sample tests)
  • Homoscedastic (equal variance assumption) or heteroscedastic (for two sample tests)
  • Fixed significance level (boolean-valued) or returning p-values.

Test statistics are available for all tests. Methods including "Test" in in their names perform tests, all other methods return t-statistics. Among the "Test" methods, double-valued methods return p-values; boolean-valued methods perform fixed significance level tests. Significance levels are always specified as numbers between 0 and 0.5 (e.g. tests at the 95% level use alpha=0.05).

Input to tests can be either double[] arrays or StatisticalSummary instances.

Uses Hipparchus TDistribution implementation to estimate exact p-values.

  • Constructor Summary

    Constructors
    Constructor
    Description
    TTest()
    Empty constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    protected double
    df(double v1, double v2, double n1, double n2)
    Computes approximate degrees of freedom for 2-sample t-test.
    double
    homoscedasticT(double[] sample1, double[] sample2)
    Computes a 2-sample t statistic, under the hypothesis of equal subpopulation variances.
    protected double
    homoscedasticT(double m1, double m2, double v1, double v2, double n1, double n2)
    Computes t test statistic for 2-sample t-test under the hypothesis of equal subpopulation variances.
    double
    homoscedasticT(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2)
    Computes a 2-sample t statistic, comparing the means of the datasets described by two StatisticalSummary instances, under the assumption of equal subpopulation variances.
    double
    homoscedasticTTest(double[] sample1, double[] sample2)
    Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the input arrays, under the assumption that the two samples are drawn from subpopulations with equal variances.
    boolean
    homoscedasticTTest(double[] sample1, double[] sample2, double alpha)
    Performs a two-sided t-test evaluating the null hypothesis that sample1 and sample2 are drawn from populations with the same mean, with significance level alpha, assuming that the subpopulation variances are equal.
    protected double
    homoscedasticTTest(double m1, double m2, double v1, double v2, double n1, double n2)
    Computes p-value for 2-sided, 2-sample t-test, under the assumption of equal subpopulation variances.
    double
    homoscedasticTTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2)
    Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the datasets described by two StatisticalSummary instances, under the hypothesis of equal subpopulation variances.
    double
    pairedT(double[] sample1, double[] sample2)
    Computes a paired, 2-sample t-statistic based on the data in the input arrays.
    double
    pairedTTest(double[] sample1, double[] sample2)
    Returns the observed significance level, or p-value, associated with a paired, two-sample, two-tailed t-test based on the data in the input arrays.
    boolean
    pairedTTest(double[] sample1, double[] sample2, double alpha)
    Performs a paired t-test evaluating the null hypothesis that the mean of the paired differences between sample1 and sample2 is 0 in favor of the two-sided alternative that the mean paired difference is not equal to 0, with significance level alpha.
    double
    t(double[] sample1, double[] sample2)
    Computes a 2-sample t statistic, without the hypothesis of equal subpopulation variances.
    double
    t(double mu, double[] observed)
    Computes a t statistic given observed values and a comparison constant.
    protected double
    t(double m, double mu, double v, double n)
    Computes t test statistic for 1-sample t-test.
    protected double
    t(double m1, double m2, double v1, double v2, double n1, double n2)
    Computes t test statistic for 2-sample t-test.
    double
    t(double mu, StatisticalSummary sampleStats)
    Computes a t statistic to use in comparing the mean of the dataset described by sampleStats to mu.
    double
    t(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2)
    Computes a 2-sample t statistic, comparing the means of the datasets described by two StatisticalSummary instances, without the assumption of equal subpopulation variances.
    double
    tTest(double[] sample1, double[] sample2)
    Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the input arrays.
    boolean
    tTest(double[] sample1, double[] sample2, double alpha)
    Performs a two-sided t-test evaluating the null hypothesis that sample1 and sample2 are drawn from populations with the same mean, with significance level alpha.
    double
    tTest(double mu, double[] sample)
    Returns the observed significance level, or p-value, associated with a one-sample, two-tailed t-test comparing the mean of the input array with the constant mu.
    boolean
    tTest(double mu, double[] sample, double alpha)
    Performs a two-sided t-test evaluating the null hypothesis that the mean of the population from which sample is drawn equals mu.
    protected double
    tTest(double m, double mu, double v, double n)
    Computes p-value for 2-sided, 1-sample t-test.
    protected double
    tTest(double m1, double m2, double v1, double v2, double n1, double n2)
    Computes p-value for 2-sided, 2-sample t-test.
    double
    tTest(double mu, StatisticalSummary sampleStats)
    Returns the observed significance level, or p-value, associated with a one-sample, two-tailed t-test comparing the mean of the dataset described by sampleStats with the constant mu.
    boolean
    tTest(double mu, StatisticalSummary sampleStats, double alpha)
    Performs a two-sided t-test evaluating the null hypothesis that the mean of the population from which the dataset described by stats is drawn equals mu.
    double
    tTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2)
    Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the datasets described by two StatisticalSummary instances.
    boolean
    tTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2, double alpha)
    Performs a two-sided t-test evaluating the null hypothesis that sampleStats1 and sampleStats2 describe datasets drawn from populations with the same mean, with significance level alpha.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • TTest

      public TTest()
      Empty constructor.

      This constructor is not strictly necessary, but it prevents spurious javadoc warnings with JDK 18 and later.

      Since:
      3.0

  • Method Details

    • pairedT

      public double pairedT(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException
      Computes a paired, 2-sample t-statistic based on the data in the input arrays. The t-statistic returned is equivalent to what would be returned by computing the one-sample t-statistic t(double, double[]), with mu = 0 and the sample array consisting of the (signed) differences between corresponding entries in sample1 and sample2.

      * Preconditions:

      • The input arrays must have the same length and their common length must be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      t statistic
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the arrays are empty
      MathIllegalArgumentException - if the length of the arrays is not equal
      MathIllegalArgumentException - if the length of the arrays is < 2

    • pairedTTest

      public double pairedTTest(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a paired, two-sample, two-tailed t-test based on the data in the input arrays.

      The number returned is the smallest significance level at which one can reject the null hypothesis that the mean of the paired differences is 0 in favor of the two-sided alternative that the mean paired difference is not equal to 0. For a one-sided test, divide the returned value by 2.

      This test is equivalent to a one-sample t-test computed using tTest(double, double[]) with mu = 0 and the sample array consisting of the signed differences between corresponding elements of sample1 and sample2.

      Usage Note:
      The validity of the p-value depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The input array lengths must be the same and their common length must be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      p-value for t-test
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the arrays are empty
      MathIllegalArgumentException - if the length of the arrays is not equal
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • pairedTTest

      public boolean pairedTTest(double[] sample1, double[] sample2, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a paired t-test evaluating the null hypothesis that the mean of the paired differences between sample1 and sample2 is 0 in favor of the two-sided alternative that the mean paired difference is not equal to 0, with significance level alpha.

      Returns true iff the null hypothesis can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The input array lengths must be the same and their common length must be at least 2.
      • 0 < alpha < 0.5
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      alpha - significance level of the test
      Returns:
      true if the null hypothesis can be rejected with confidence 1 - alpha
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the arrays are empty
      MathIllegalArgumentException - if the length of the arrays is not equal
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error occurs computing the p-value

    • t

      public double t(double mu, double[] observed) throws MathIllegalArgumentException, NullArgumentException
      Computes a t statistic given observed values and a comparison constant.

      This statistic can be used to perform a one sample t-test for the mean.

      Preconditions:

      • The observed array length must be at least 2.
      Parameters:
      mu - comparison constant
      observed - array of values
      Returns:
      t statistic
      Throws:
      NullArgumentException - if observed is null
      MathIllegalArgumentException - if the length of observed is < 2

    • t

      public double t(double mu, StatisticalSummary sampleStats) throws MathIllegalArgumentException, NullArgumentException
      Computes a t statistic to use in comparing the mean of the dataset described by sampleStats to mu.

      This statistic can be used to perform a one sample t-test for the mean.

      Preconditions:

      • observed.getN() ≥ 2.
      Parameters:
      mu - comparison constant
      sampleStats - DescriptiveStatistics holding sample summary statitstics
      Returns:
      t statistic
      Throws:
      NullArgumentException - if sampleStats is null
      MathIllegalArgumentException - if the number of samples is < 2

    • homoscedasticT

      public double homoscedasticT(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException
      Computes a 2-sample t statistic, under the hypothesis of equal subpopulation variances. To compute a t-statistic without the equal variances hypothesis, use t(double[], double[]).

      This statistic can be used to perform a (homoscedastic) two-sample t-test to compare sample means.

      The t-statistic is

         t = (m1 - m2) / (sqrt(1/n1 +1/n2) sqrt(var))

      where n1 is the size of first sample; n2 is the size of second sample; m1 is the mean of first sample; m2 is the mean of second sample and var is the pooled variance estimate:

      var = sqrt(((n1 - 1)var1 + (n2 - 1)var2) / ((n1-1) + (n2-1)))

      with var1 the variance of the first sample and var2 the variance of the second sample.

      Preconditions:

      • The observed array lengths must both be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      t statistic
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2

    • t

      public double t(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException
      Computes a 2-sample t statistic, without the hypothesis of equal subpopulation variances. To compute a t-statistic assuming equal variances, use homoscedasticT(double[], double[]).

      This statistic can be used to perform a two-sample t-test to compare sample means.

      The t-statistic is

         t = (m1 - m2) / sqrt(var1/n1 + var2/n2)

      where n1 is the size of the first sample n2 is the size of the second sample; m1 is the mean of the first sample; m2 is the mean of the second sample; var1 is the variance of the first sample; var2 is the variance of the second sample;

      Preconditions:

      • The observed array lengths must both be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      t statistic
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2

    • t

      public double t(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2) throws MathIllegalArgumentException, NullArgumentException
      Computes a 2-sample t statistic, comparing the means of the datasets described by two StatisticalSummary instances, without the assumption of equal subpopulation variances. Use homoscedasticT(StatisticalSummary, StatisticalSummary) to compute a t-statistic under the equal variances assumption.

      This statistic can be used to perform a two-sample t-test to compare sample means.

      The returned t-statistic is

         t = (m1 - m2) / sqrt(var1/n1 + var2/n2)

      where n1 is the size of the first sample; n2 is the size of the second sample; m1 is the mean of the first sample; m2 is the mean of the second sample var1 is the variance of the first sample; var2 is the variance of the second sample

      Preconditions:

      • The datasets described by the two Univariates must each contain at least 2 observations.
      Parameters:
      sampleStats1 - StatisticalSummary describing data from the first sample
      sampleStats2 - StatisticalSummary describing data from the second sample
      Returns:
      t statistic
      Throws:
      NullArgumentException - if the sample statistics are null
      MathIllegalArgumentException - if the number of samples is < 2

    • homoscedasticT

      public double homoscedasticT(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2) throws MathIllegalArgumentException, NullArgumentException
      Computes a 2-sample t statistic, comparing the means of the datasets described by two StatisticalSummary instances, under the assumption of equal subpopulation variances. To compute a t-statistic without the equal variances assumption, use t(StatisticalSummary, StatisticalSummary).

      This statistic can be used to perform a (homoscedastic) two-sample t-test to compare sample means.

      The t-statistic returned is

         t = (m1 - m2) / (sqrt(1/n1 +1/n2) sqrt(var))

      where n1 is the size of first sample; n2 is the size of second sample; m1 is the mean of first sample; m2 is the mean of second sample and var is the pooled variance estimate:

      var = sqrt(((n1 - 1)var1 + (n2 - 1)var2) / ((n1-1) + (n2-1)))

      with var1 the variance of the first sample and var2 the variance of the second sample.

      Preconditions:

      • The datasets described by the two Univariates must each contain at least 2 observations.
      Parameters:
      sampleStats1 - StatisticalSummary describing data from the first sample
      sampleStats2 - StatisticalSummary describing data from the second sample
      Returns:
      t statistic
      Throws:
      NullArgumentException - if the sample statistics are null
      MathIllegalArgumentException - if the number of samples is < 2

    • tTest

      public double tTest(double mu, double[] sample) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a one-sample, two-tailed t-test comparing the mean of the input array with the constant mu.

      The number returned is the smallest significance level at which one can reject the null hypothesis that the mean equals mu in favor of the two-sided alternative that the mean is different from mu. For a one-sided test, divide the returned value by 2.

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array length must be at least 2.
      Parameters:
      mu - constant value to compare sample mean against
      sample - array of sample data values
      Returns:
      p-value
      Throws:
      NullArgumentException - if the sample array is null
      MathIllegalArgumentException - if the length of the array is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public boolean tTest(double mu, double[] sample, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a two-sided t-test evaluating the null hypothesis that the mean of the population from which sample is drawn equals mu.

      Returns true iff the null hypothesis can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2

      * Examples:

      1. To test the (2-sided) hypothesis sample mean = mu at the 95% level, use
        tTest(mu, sample, 0.05)
      2. To test the (one-sided) hypothesis sample mean < mu at the 99% level, first verify that the measured sample mean is less than mu and then use
        tTest(mu, sample, 0.02)

      Usage Note:
      The validity of the test depends on the assumptions of the one-sample parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array length must be at least 2.
      Parameters:
      mu - constant value to compare sample mean against
      sample - array of sample data values
      alpha - significance level of the test
      Returns:
      p-value
      Throws:
      NullArgumentException - if the sample array is null
      MathIllegalArgumentException - if the length of the array is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error computing the p-value

    • tTest

      public double tTest(double mu, StatisticalSummary sampleStats) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a one-sample, two-tailed t-test comparing the mean of the dataset described by sampleStats with the constant mu.

      The number returned is the smallest significance level at which one can reject the null hypothesis that the mean equals mu in favor of the two-sided alternative that the mean is different from mu. For a one-sided test, divide the returned value by 2.

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The sample must contain at least 2 observations.
      Parameters:
      mu - constant value to compare sample mean against
      sampleStats - StatisticalSummary describing sample data
      Returns:
      p-value
      Throws:
      NullArgumentException - if sampleStats is null
      MathIllegalArgumentException - if the number of samples is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public boolean tTest(double mu, StatisticalSummary sampleStats, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a two-sided t-test evaluating the null hypothesis that the mean of the population from which the dataset described by stats is drawn equals mu.

      Returns true iff the null hypothesis can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2.

      * Examples:

      1. To test the (2-sided) hypothesis sample mean = mu at the 95% level, use
        tTest(mu, sampleStats, 0.05)
      2. To test the (one-sided) hypothesis sample mean < mu at the 99% level, first verify that the measured sample mean is less than mu and then use
        tTest(mu, sampleStats, 0.02)

      Usage Note:
      The validity of the test depends on the assumptions of the one-sample parametric t-test procedure, as discussed here

      Preconditions:

      • The sample must include at least 2 observations.
      Parameters:
      mu - constant value to compare sample mean against
      sampleStats - StatisticalSummary describing sample data values
      alpha - significance level of the test
      Returns:
      p-value
      Throws:
      NullArgumentException - if sampleStats is null
      MathIllegalArgumentException - if the number of samples is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public double tTest(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the input arrays.

      The number returned is the smallest significance level at which one can reject the null hypothesis that the two means are equal in favor of the two-sided alternative that they are different. For a one-sided test, divide the returned value by 2.

      The test does not assume that the underlying popuation variances are equal and it uses approximated degrees of freedom computed from the sample data to compute the p-value. The t-statistic used is as defined in t(double[], double[]) and the Welch-Satterthwaite approximation to the degrees of freedom is used, as described here. To perform the test under the assumption of equal subpopulation variances, use homoscedasticTTest(double[], double[]).

      Usage Note:
      The validity of the p-value depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array lengths must both be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      p-value for t-test
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • homoscedasticTTest

      public double homoscedasticTTest(double[] sample1, double[] sample2) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the input arrays, under the assumption that the two samples are drawn from subpopulations with equal variances. To perform the test without the equal variances assumption, use tTest(double[], double[]).

      The number returned is the smallest significance level at which one can reject the null hypothesis that the two means are equal in favor of the two-sided alternative that they are different. For a one-sided test, divide the returned value by 2.

      A pooled variance estimate is used to compute the t-statistic. See homoscedasticT(double[], double[]). The sum of the sample sizes minus 2 is used as the degrees of freedom.

      Usage Note:
      The validity of the p-value depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array lengths must both be at least 2.
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      Returns:
      p-value for t-test
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public boolean tTest(double[] sample1, double[] sample2, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a two-sided t-test evaluating the null hypothesis that sample1 and sample2 are drawn from populations with the same mean, with significance level alpha. This test does not assume that the subpopulation variances are equal. To perform the test assuming equal variances, use homoscedasticTTest(double[], double[], double).

      Returns true iff the null hypothesis that the means are equal can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2

      See t(double[], double[]) for the formula used to compute the t-statistic. Degrees of freedom are approximated using the Welch-Satterthwaite approximation.

      * Examples:

      1. To test the (2-sided) hypothesis mean 1 = mean 2 at the 95% level, use
        tTest(sample1, sample2, 0.05).
      2. To test the (one-sided) hypothesis mean 1 < mean 2 , at the 99% level, first verify that the measured mean of sample 1 is less than the mean of sample 2 and then use
        tTest(sample1, sample2, 0.02)

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array lengths must both be at least 2.
      • 0 < alpha < 0.5
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      alpha - significance level of the test
      Returns:
      true if the null hypothesis can be rejected with confidence 1 - alpha
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error occurs computing the p-value

    • homoscedasticTTest

      public boolean homoscedasticTTest(double[] sample1, double[] sample2, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a two-sided t-test evaluating the null hypothesis that sample1 and sample2 are drawn from populations with the same mean, with significance level alpha, assuming that the subpopulation variances are equal. Use tTest(double[], double[], double) to perform the test without the assumption of equal variances.

      Returns true iff the null hypothesis that the means are equal can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2. To perform the test without the assumption of equal subpopulation variances, use tTest(double[], double[], double).

      A pooled variance estimate is used to compute the t-statistic. See t(double[], double[]) for the formula. The sum of the sample sizes minus 2 is used as the degrees of freedom.

      Examples:

      1. To test the (2-sided) hypothesis mean 1 = mean 2 at the 95% level, use
        tTest(sample1, sample2, 0.05).
      2. To test the (one-sided) hypothesis mean 1 < mean 2, at the 99% level, first verify that the measured mean of sample 1 is less than the mean of sample 2 and then use
        tTest(sample1, sample2, 0.02)

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The observed array lengths must both be at least 2.
      • 0 < alpha < 0.5
      Parameters:
      sample1 - array of sample data values
      sample2 - array of sample data values
      alpha - significance level of the test
      Returns:
      true if the null hypothesis can be rejected with confidence 1 - alpha
      Throws:
      NullArgumentException - if the arrays are null
      MathIllegalArgumentException - if the length of the arrays is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public double tTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the datasets described by two StatisticalSummary instances.

      The number returned is the smallest significance level at which one can reject the null hypothesis that the two means are equal in favor of the two-sided alternative that they are different. For a one-sided test, divide the returned value by 2.

      The test does not assume that the underlying population variances are equal and it uses approximated degrees of freedom computed from the sample data to compute the p-value. To perform the test assuming equal variances, use homoscedasticTTest(StatisticalSummary, StatisticalSummary).

      Usage Note:
      The validity of the p-value depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The datasets described by the two Univariates must each contain at least 2 observations.
      Parameters:
      sampleStats1 - StatisticalSummary describing data from the first sample
      sampleStats2 - StatisticalSummary describing data from the second sample
      Returns:
      p-value for t-test
      Throws:
      NullArgumentException - if the sample statistics are null
      MathIllegalArgumentException - if the number of samples is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • homoscedasticTTest

      public double homoscedasticTTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Returns the observed significance level, or p-value, associated with a two-sample, two-tailed t-test comparing the means of the datasets described by two StatisticalSummary instances, under the hypothesis of equal subpopulation variances. To perform a test without the equal variances assumption, use tTest(StatisticalSummary, StatisticalSummary).

      The number returned is the smallest significance level at which one can reject the null hypothesis that the two means are equal in favor of the two-sided alternative that they are different. For a one-sided test, divide the returned value by 2.

      See homoscedasticT(double[], double[]) for the formula used to compute the t-statistic. The sum of the sample sizes minus 2 is used as the degrees of freedom.

      Usage Note:
      The validity of the p-value depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The datasets described by the two Univariates must each contain at least 2 observations.
      Parameters:
      sampleStats1 - StatisticalSummary describing data from the first sample
      sampleStats2 - StatisticalSummary describing data from the second sample
      Returns:
      p-value for t-test
      Throws:
      NullArgumentException - if the sample statistics are null
      MathIllegalArgumentException - if the number of samples is < 2
      MathIllegalStateException - if an error occurs computing the p-value

    • tTest

      public boolean tTest(StatisticalSummary sampleStats1, StatisticalSummary sampleStats2, double alpha) throws MathIllegalArgumentException, NullArgumentException, MathIllegalStateException
      Performs a two-sided t-test evaluating the null hypothesis that sampleStats1 and sampleStats2 describe datasets drawn from populations with the same mean, with significance level alpha. This test does not assume that the subpopulation variances are equal. To perform the test under the equal variances assumption, use homoscedasticTTest(StatisticalSummary, StatisticalSummary).

      Returns true iff the null hypothesis that the means are equal can be rejected with confidence 1 - alpha. To perform a 1-sided test, use alpha * 2

      See t(double[], double[]) for the formula used to compute the t-statistic. Degrees of freedom are approximated using the Welch-Satterthwaite approximation.

      * Examples:

      1. To test the (2-sided) hypothesis mean 1 = mean 2 at the 95%, use
        tTest(sampleStats1, sampleStats2, 0.05)
      2. To test the (one-sided) hypothesis mean 1 < mean 2 at the 99% level, first verify that the measured mean of sample 1 is less than the mean of sample 2 and then use
        tTest(sampleStats1, sampleStats2, 0.02)

      Usage Note:
      The validity of the test depends on the assumptions of the parametric t-test procedure, as discussed here

      Preconditions:

      • The datasets described by the two Univariates must each contain at least 2 observations.
      • 0 < alpha < 0.5
      Parameters:
      sampleStats1 - StatisticalSummary describing sample data values
      sampleStats2 - StatisticalSummary describing sample data values
      alpha - significance level of the test
      Returns:
      true if the null hypothesis can be rejected with confidence 1 - alpha
      Throws:
      NullArgumentException - if the sample statistics are null
      MathIllegalArgumentException - if the number of samples is < 2
      MathIllegalArgumentException - if alpha is not in the range (0, 0.5]
      MathIllegalStateException - if an error occurs computing the p-value

    • df

      protected double df(double v1, double v2, double n1, double n2)
      Computes approximate degrees of freedom for 2-sample t-test.
      Parameters:
      v1 - first sample variance
      v2 - second sample variance
      n1 - first sample n
      n2 - second sample n
      Returns:
      approximate degrees of freedom

    • t

      protected double t(double m, double mu, double v, double n)
      Computes t test statistic for 1-sample t-test.
      Parameters:
      m - sample mean
      mu - constant to test against
      v - sample variance
      n - sample n
      Returns:
      t test statistic

    • t

      protected double t(double m1, double m2, double v1, double v2, double n1, double n2)
      Computes t test statistic for 2-sample t-test.

      Does not assume that subpopulation variances are equal.

      Parameters:
      m1 - first sample mean
      m2 - second sample mean
      v1 - first sample variance
      v2 - second sample variance
      n1 - first sample n
      n2 - second sample n
      Returns:
      t test statistic

    • homoscedasticT

      protected double homoscedasticT(double m1, double m2, double v1, double v2, double n1, double n2)
      Computes t test statistic for 2-sample t-test under the hypothesis of equal subpopulation variances.
      Parameters:
      m1 - first sample mean
      m2 - second sample mean
      v1 - first sample variance
      v2 - second sample variance
      n1 - first sample n
      n2 - second sample n
      Returns:
      t test statistic

    • tTest

      protected double tTest(double m, double mu, double v, double n) throws MathIllegalArgumentException, MathIllegalStateException
      Computes p-value for 2-sided, 1-sample t-test.
      Parameters:
      m - sample mean
      mu - constant to test against
      v - sample variance
      n - sample n
      Returns:
      p-value
      Throws:
      MathIllegalStateException - if an error occurs computing the p-value
      MathIllegalArgumentException - if n is not greater than 1

    • tTest

      protected double tTest(double m1, double m2, double v1, double v2, double n1, double n2) throws MathIllegalArgumentException, MathIllegalStateException
      Computes p-value for 2-sided, 2-sample t-test.

      Does not assume subpopulation variances are equal. Degrees of freedom are estimated from the data.

      Parameters:
      m1 - first sample mean
      m2 - second sample mean
      v1 - first sample variance
      v2 - second sample variance
      n1 - first sample n
      n2 - second sample n
      Returns:
      p-value
      Throws:
      MathIllegalStateException - if an error occurs computing the p-value
      MathIllegalArgumentException - if the estimated degrees of freedom is not strictly positive

    • homoscedasticTTest

      protected double homoscedasticTTest(double m1, double m2, double v1, double v2, double n1, double n2) throws MathIllegalArgumentException, MathIllegalStateException
      Computes p-value for 2-sided, 2-sample t-test, under the assumption of equal subpopulation variances.

      The sum of the sample sizes minus 2 is used as degrees of freedom.

      Parameters:
      m1 - first sample mean
      m2 - second sample mean
      v1 - first sample variance
      v2 - second sample variance
      n1 - first sample n
      n2 - second sample n
      Returns:
      p-value
      Throws:
      MathIllegalStateException - if an error occurs computing the p-value
      MathIllegalArgumentException - if the estimated degrees of freedom is not strictly positive