Variance Tests in Visual Basic QuickStart Sample

Illustrates how to perform hypothesis tests involving the standard deviation or variance using classes in our .NET statistical library in Visual Basic.

View this sample in: C# F# IronPython

Option Infer On

Imports Numerics.NET
Imports Numerics.NET.Statistics
Imports Numerics.NET.Statistics.Tests

    ' Demonstrates how to use hypothesis tests for the variance 
    ' of one or two distributions.
    Module VarianceTests

        Sub Main()
        ' The license is verified at runtime. We're using
        ' a 30 day trial key here. For more information, see
        '     https://numerics.net/trial-key
        Numerics.NET.License.Verify("64542-18980-57619-62268")

        ' This QuickStart Sample uses the scores obtained by the students
        ' in two groups of students on a national test.
        ' 
        ' We want to know if the variance of the scores is greater than
        ' a specific value. We use the one sample Chi-square test for this
        ' purpose.

        Console.WriteLine("Tests for class 1")

        ' First we create a NumericalVariable that holds the test results.
        Dim group1Results = Vector.Create(Of Double)(
                62, 77, 61, 94, 75, 82, 86, 83, 64, 84,
                68, 82, 72, 71, 85, 66, 61, 79, 81, 73)

        ' We can get the mean and standard deviation of the class right away:
        Console.WriteLine($"Mean for the class: {group1Results.Mean:F1}")
        Console.WriteLine($"Standard deviation: {group1Results.StandardDeviation:F1}")

        '
        ' One Sample Chi-square Test
        '

        Console.WriteLine(Environment.NewLine + "Using chi-square test:")

        ' We want to know if the variance is larger than 5.
        ' Therefore, we use a one-tailed chi-square test:
        Dim chiSquareTest As OneSampleChiSquareTest =
                New OneSampleChiSquareTest(group1Results, 5, HypothesisType.OneTailedUpper)

        ' We can obtan the value of the test statistic through the Statistic property,
        ' and the corresponding P-value through the Probability property:
        Console.WriteLine($"Test statistic: {chiSquareTest.Statistic:F4}")
        Console.WriteLine($"P-value:        {chiSquareTest.PValue:F4}")

        ' The significance level is the default value of 0.05:
        Console.WriteLine("Significance level:     {0:F2}",
                chiSquareTest.SignificanceLevel)
        ' We can now print the test results:
        Console.WriteLine("Reject null hypothesis? {0}",
                If(chiSquareTest.Reject(), "yes", "no"))
        ' We can get a confidence interval for the current significance level:
        Dim varianceInterval As Interval = chiSquareTest.GetConfidenceInterval()
        Console.WriteLine("95% Confidence interval for the variance: {0:F1} - {1:F1}",
                varianceInterval.LowerBound, varianceInterval.UpperBound)

        ' We can get the same results for the 0.01 significance level by explicitly
        ' passing the significance level as a parameter to these methods:
        Console.WriteLine($"Significance level:     {0.01:F2}")
        Console.WriteLine("Reject null hypothesis? {0}",
                If(chiSquareTest.Reject(0.01), "yes", "no"))

        ' The GetConfidenceInterval method needs the confidence level, which equals
        ' 1 - the significance level:
        varianceInterval = chiSquareTest.GetConfidenceInterval(0.99)
        Console.WriteLine("99% Confidence interval for the variance: {0:F1} - {1:F1}",
                varianceInterval.LowerBound, varianceInterval.UpperBound)

        ' 
        ' Two sample F-test
        '

        Console.WriteLine(Environment.NewLine + "Using F-test:")
        ' We want to compare the scores of the first group to the scores 
        ' of a second group from another school. We want to verify that the
        ' variances of the scores from the two schools are equal. Once again, 
        ' we start by creating a NumericalVariable, this time containing 
        ' the scores for the second group:
        Dim group2Results = Vector.Create(Of Double)(
                61, 80, 98, 90, 94, 65, 79, 75, 74, 86,
                76, 85, 78, 72, 76, 79, 65, 92, 76, 80)

        ' To compare the variances of the two groups, we need the two sample
        ' F test, implemented by the FTest class:
        Dim fTest As FTest = New FTest(group1Results, group2Results)
        ' We can obtan the value of the test statistic through the Statistic property,
        ' and the corresponding P-value through the Probability property:
        Console.WriteLine($"Test statistic: {fTest.Statistic:F4}")
        Console.WriteLine($"P-value:        {fTest.PValue:F4}")

        ' The significance level is the default value of 0.05:
        Console.WriteLine("Significance level:     {0:F2}",
                fTest.SignificanceLevel)
        ' We can now print the test results:
        Console.WriteLine("Reject null hypothesis? {0}",
                If(fTest.Reject(), "yes", "no"))

        Console.Write("Press any key to exit.")
        Console.ReadLine()

    End Sub

End Module