Fixed a bug where contrasts with negative T where incorrectly processed.

Planned contrasts in the ONEWAY procedure reported p-values > 1 when
T was negative.  This change fixes this problem.

Thanks to Douglas Bonett <dgbonett@ucsc.edu> for reporting this.

diff --git a/NEWS b/NEWS
index 76c0913f887d6fc1b09812a093cdb29eed4f7d82..f44ab7774d9e03cfab1b59376e173120667fa965 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,11 @@ See the end for copying conditions.
 
 Please send PSPP bug reports to bug-gnu-pspp@gnu.org.
  
+Changes from 0.8.2 to 0.8.3.1:
+
+ * Fixed a bug where planned comparisons in oneway anova did not correctly
+   handle negative T-values.
+
 Changes from 0.8.2 to 0.8.3:
 
  * Independent T-Tests displayed the standard error of the difference

diff --git a/src/language/stats/oneway.c b/src/language/stats/oneway.c
index 807b5dc39f10b6e8bc5f2af2eb8637b97a4796b6..a64b760eb9174ab0ac0c61821c16a2fd4b8589c2 100644 (file)
--- a/src/language/stats/oneway.c
+++ b/src/language/stats/oneway.c
@@ -1528,10 +1528,15 @@ show_contrast_tests (const struct oneway_spec *cmd, const struct oneway_workspac
                      TAB_RIGHT, df,
                      NULL);
 
-         /* The Significance */
-         tab_double (t, 7, (v * lines_per_variable) + i + 1 + n_contrasts,
-                     TAB_RIGHT,  2 * gsl_cdf_tdist_Q (T,df),
-                     NULL);
+         {
+           double p = gsl_cdf_tdist_P (T, df);
+           double q = gsl_cdf_tdist_Q (T, df);
+
+           /* The Significance */
+           tab_double (t, 7, (v * lines_per_variable) + i + 1 + n_contrasts,
+                       TAB_RIGHT,  2 * ((T > 0) ? q : p),
+                       NULL);
+         }
        }
 
       if ( v > 0 )

diff --git a/tests/language/stats/oneway.at b/tests/language/stats/oneway.at
index 16c2b55b9c0fe2dfd6b9f6f11788fcd141bba67c..03e8145d160ed55c721d85d7068a8dee9249a471 100644 (file)
--- a/tests/language/stats/oneway.at
+++ b/tests/language/stats/oneway.at
@@ -464,15 +464,15 @@ Table: Contrast Tests
 ,,Contrast,Value of Contrast,Std. Error,t,df,Sig. (2-tailed)
 x,Assume equal variances,1,-7.40,6.67,1.11,20,.28
 ,,2,6.26,12.32,.51,20,.62
-,Does not assume equal,1,-7.40,10.04,-.74,4.53,1.50
+,Does not assume equal,1,-7.40,10.04,-.74,4.53,.50
 ,,2,6.26,5.85,1.07,2.87,.37
 y,Assume equal variances,1,-6.88,1.16,5.94,20,.00
 ,,2,3.50,2.14,1.63,20,.12
-,Does not assume equal,1,-6.88,.91,-7.51,7.00,2.00
+,Does not assume equal,1,-6.88,.91,-7.51,7.00,.00
 ,,2,3.50,1.32,2.65,7.00,.03
 z,Assume equal variances,1,-9.70,8.07,1.20,20,.24
 ,,2,11.73,14.91,.79,20,.44
-,Does not assume equal,1,-9.70,9.57,-1.01,3.64,1.63
+,Does not assume equal,1,-9.70,9.57,-1.01,3.64,.37
 ,,2,11.73,14.53,.81,9.88,.44
 ])
 
@@ -883,21 +883,21 @@ Table: Contrast Tests
 height,Assume equal variances,1,-222.27,20.23,10.99,6,.00
 ,,2,-666.80,60.68,10.99,6,.00
 ,,3,-2000.40,182.03,10.99,6,.00
-,Does not assume equal,1,-222.27,27.67,-8.03,2.00,1.98
-,,2,-666.80,83.02,-8.03,2.00,1.98
-,,3,-2000.40,249.07,-8.03,2.00,1.98
+,Does not assume equal,1,-222.27,27.67,-8.03,2.00,.02
+,,2,-666.80,83.02,-8.03,2.00,.02
+,,3,-2000.40,249.07,-8.03,2.00,.02
 weight,Assume equal variances,1,-36.16,2.74,13.21,6,.00
 ,,2,-108.48,8.21,13.21,6,.00
 ,,3,-325.44,24.63,13.21,6,.00
-,Does not assume equal,1,-36.16,2.19,-16.48,5.42,2.00
-,,2,-108.48,6.58,-16.48,5.42,2.00
-,,3,-325.44,19.75,-16.48,5.42,2.00
+,Does not assume equal,1,-36.16,2.19,-16.48,5.42,.00
+,,2,-108.48,6.58,-16.48,5.42,.00
+,,3,-325.44,19.75,-16.48,5.42,.00
 temperature,Assume equal variances,1,-.98,2.74,.36,6,.73
 ,,2,-2.94,8.22,.36,6,.73
 ,,3,-8.83,24.67,.36,6,.73
-,Does not assume equal,1,-.98,2.07,-.47,4.19,1.34
-,,2,-2.94,6.22,-.47,4.19,1.34
-,,3,-8.83,18.66,-.47,4.19,1.34
+,Does not assume equal,1,-.98,2.07,-.47,4.19,.66
+,,2,-2.94,6.22,-.47,4.19,.66
+,,3,-8.83,18.66,-.47,4.19,.66
 ])
 
 AT_CLEANUP