Changeset 10016 for branches/StatisticalTesting/HeuristicLab.Analysis.Statistics/3.3/SampleSizeDetermination.cs

Timestamp:

10/01/13 21:42:07 (11 years ago)

Author:

ascheibe

Message:

#2031 added recommended sample size to sample size influence view

File:

• branches/StatisticalTesting/HeuristicLab.Analysis.Statistics/3.3/SampleSizeDetermination.cs (modified) (1 diff)

branches/StatisticalTesting/HeuristicLab.Analysis.Statistics/3.3/SampleSizeDetermination.cs

@@ -27 +27 @@
   public class SampleSizeDetermination {
     /// <summary>
-    /// Determines for a given sample the sample size by estimating the means. 
+    /// Determines for a given sample the required sample size as described in 
+    /// Göran Kauermann, Helmut Küchenhoff: Stichproben: Methoden und praktische Umsetzung mit R, chapter 2.27. 
     /// </summary>
     /// <param name="samples">The pilot sample.</param>
-    /// <param name="e">Precision. </param>
     /// <param name="conf">Confidence Interval.</param>
     /// <returns>Number of required samples for the given confidence interval and precision. </returns>
-    public static int DetermineSampleSizeByEstimatingMean(double[] samples, double e, double conf = 0.95) {
-      if (e < 0) throw new ArgumentException("e needs to be a positive number.");
+    public static int DetermineSampleSizeByEstimatingMean(double[] samples, double conf = 0.95) {
       if (conf < 0 || conf > 1) throw new ArgumentException("The confidence Interval must be between zero and one.");
-      double result = 0;
 
-      double var = samples.StandardDeviation();
-      double n = alglib.invnormaldistribution((conf + 1) / 2);
-      result = Math.Pow(n, 2) * Math.Pow(var, 2) / Math.Pow(e, 2);
+      var confInterval = samples.ConfidenceIntervals(0.95);
+      double e = (confInterval.Item2 - confInterval.Item1) / 2;
+      double s = samples.StandardDeviation();
+      double z = alglib.invnormaldistribution((conf + 1) / 2);
+      double n = samples.Count();
+
+      double result = Math.Pow(s, 2) / ((Math.Pow(e, 2) / Math.Pow(z, 2)) + (Math.Pow(s, 2) / n));
+
       result = Math.Ceiling(result);
       if (result > int.MaxValue)