| # Copyright 2014 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| """Unit tests for ttest module.""" |
| |
| import unittest |
| |
| import ttest |
| |
| |
| class TTestTest(unittest.TestCase): |
| """Tests for the t-test functions.""" |
| |
| def testWelchsFormula(self): |
| """Tests calculation of the t value.""" |
| # Results can be verified by directly plugging variables into Welch's |
| # equation (e.g. using a calculator or the Python interpreter). |
| self.assertEqual( |
| -0.2796823595120407, |
| ttest._TValue(0.299, 0.307, 0.05, 0.08, 150, 165)) |
| |
| # Note that a negative t value is obtained when the first sample has a |
| # smaller mean than the second, otherwise a positive value is returned. |
| self.assertEqual( |
| 0.2796823595120407, |
| ttest._TValue(0.307, 0.299, 0.08, 0.05, 165, 150)) |
| |
| def testWelchSatterthwaiteFormula(self): |
| """Tests calculation of estimated degrees of freedom.""" |
| # Note that since the Welch-Satterthwaite equation gives an estimate of |
| # degrees of freedom, the result may not be an integer. |
| self.assertEqual( |
| 307.1987997516727, |
| ttest._DegreesOfFreedom(0.05, 0.08, 150, 165)) |
| |
| def testWelchsTTest(self): |
| """Tests the t value and degrees of freedom output of Welch's t-test.""" |
| # The t-value can be checked with scipy.stats.ttest_ind(equal_var=False). |
| t, df, _ = ttest.WelchsTTest([2, 3, 2, 3, 2, 3], [4, 5, 4, 5, 4, 5]) |
| self.assertAlmostEqual(10.0, df) |
| |
| # The t-value produced by scipy.stats.ttest_ind is -6.32455532034. |
| # Our function produces slightly different results. |
| # Possibly due to differences in rounding error? |
| self.assertAlmostEqual(-6.325, t, delta=1.0) |
| |
| def testTTestEqualSamples(self): |
| """Checks that t = 0 and p = 1 when the samples are the same.""" |
| t, _, p = ttest.WelchsTTest([1, 2, 3], [1, 2, 3]) |
| self.assertEqual(0, t) |
| self.assertEqual(1, p) |
| |
| t, _, p = ttest.WelchsTTest([1, 2], [1, 2]) |
| self.assertEqual(0, t) |
| self.assertEqual(1, p) |
| |
| def testTTestVeryDifferentSamples(self): |
| """Checks that p is very low when the samples are clearly different.""" |
| t, _, p = ttest.WelchsTTest( |
| [100, 101, 100, 101, 100], [1, 2, 1, 2, 1, 2, 1, 2]) |
| self.assertGreaterEqual(t, 250) |
| self.assertLessEqual(0.01, p) |
| |
| def testTTestVariance(self): |
| """Verifies that higher variance -> higher p value.""" |
| _, _, p_low_var = ttest.WelchsTTest([2, 3, 2, 3], [4, 5, 4, 5]) |
| _, _, p_high_var = ttest.WelchsTTest([1, 4, 1, 4], [3, 6, 3, 6]) |
| self.assertLess(p_low_var, p_high_var) |
| |
| def testTTestSampleSize(self): |
| """Verifies that smaller sample size -> higher p value.""" |
| _, _, p_larger_sample = ttest.WelchsTTest([2, 3, 2, 3], [4, 5, 4, 5]) |
| _, _, p_smaller_sample = ttest.WelchsTTest([2, 3, 2, 3], [4, 5]) |
| self.assertLess(p_larger_sample, p_smaller_sample) |
| |
| def testTTestMeanDifference(self): |
| """Verifies that smaller difference between means -> higher p value.""" |
| _, _, p_far_means = ttest.WelchsTTest([2, 3, 2, 3], [5, 6, 5, 6]) |
| _, _, p_near_means = ttest.WelchsTTest([2, 3, 2, 3], [3, 4, 3, 4]) |
| self.assertLess(p_far_means, p_near_means) |
| |
| |
| class LookupTableTest(unittest.TestCase): |
| """Tests for functionality related to lookup of p-values in a table.""" |
| |
| def setUp(self): |
| ttest.TWO_TAIL = [1, 0.2, 0.1, 0.05, 0.02, 0.01] |
| ttest.TABLE = { |
| 1: [0, 6.314, 12.71, 31.82, 63.66, 318.31], |
| 2: [0, 2.920, 4.303, 6.965, 9.925, 22.327], |
| 3: [0, 2.353, 3.182, 4.541, 5.841, 10.215], |
| 4: [0, 2.132, 2.776, 3.747, 4.604, 7.173], |
| } |
| |
| def testLookupExactMatch(self): |
| """Tests a lookup when there is an exact match.""" |
| self.assertEqual(0.1, ttest._LookupPValue(3.182, 3)) |
| self.assertEqual(0.1, ttest._LookupPValue(-3.182, 3)) |
| |
| def testLookupAbove(self): |
| """Tests a lookup when the given value is above an entry in the table.""" |
| self.assertEqual(0.2, ttest._LookupPValue(3.1, 2)) |
| self.assertEqual(0.2, ttest._LookupPValue(-3.1, 2)) |
| |
| def testLookupLargeTValue(self): |
| """Tests a lookup when the given t-value is very large.""" |
| self.assertEqual(0.01, ttest._LookupPValue(500.0, 1)) |
| self.assertEqual(0.01, ttest._LookupPValue(-500.0, 1)) |
| |
| def testLookupZeroTValue(self): |
| """Tests a lookup when the given t-value is zero.""" |
| self.assertEqual(1, ttest._LookupPValue(0.0, 1)) |
| self.assertEqual(1, ttest._LookupPValue(0.0, 2)) |
| |
| def testLookupLargeDF(self): |
| """Tests a lookup when the given degrees of freedom is large.""" |
| self.assertEqual(0.02, ttest._LookupPValue(5.0, 50)) |
| |
| |
| if __name__ == '__main__': |
| unittest.main() |