C:/Documents and Settings/Stephen/Desktop/Biostatistics Library and Program/Biostatistics/ZTest.cs

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using System;

namespace StephenAshley.Biostatistics
{
   using NUMBER = Decimal;
   public class ZTest
   {
      public ZTest()
      {
         data = new ZTest.Fields(2, 2, 0.0000000000000000000000000001m, 
            0.0000000000000000000000000001m);
      }

      public ZTest(Int32 iSampleSize1, Int32 iSampleSize2, NUMBER decProportion1, 
         NUMBER decProportion2)
      {
         SetN1(iSampleSize1);
         SetN2(iSampleSize2);
         SetP1(decProportion1);
         SetP2(decProportion2);
      }

      private Fields data;

      #region ****** properties ******
      public Int32 N1()
      {
         return data.iN1;
      }

      public void SetN1(Int32 value)
      {
         if (value < 2) throw new BiostatisticsException("N1 value in ZTest less than 2.");
         data.iN1 = value;
      }

      public Int32 N2()
      {
         return data.iN2;
      }

      public void SetN2(Int32 value)
      {
         if (value < 2) throw new BiostatisticsException("N2 value in ZTest less than 2.");
         data.iN2 = value;
      }

      public NUMBER P1()
      {
         return data.decP1;
      }

      public void SetP1(NUMBER value)
      {
         if (value <= 0.0m)
            throw new BiostatisticsException("P1 value in ZTest less than 0.");
         data.decP1 = value;
      }
      public NUMBER P2()
      {
         return data.decP2;
      }
      
      public void SetP2(NUMBER value)
      {
         if (value <= 0.0m)
            throw new BiostatisticsException("P2 value in ZTest less than 0.");
         data.decP2 = value;
      }
      public NUMBER ConfidenceLevelLowerLimit()
      {
         return Difference() -
               1.959964394569397m * StandardErrorOfDifference();
      }

      public NUMBER ConfidenceLevelUpperLimit()
      {
         return Difference() + 1.959964394569397m * StandardErrorOfDifference();
      }

      public NUMBER Difference() { return P1() - P2(); }

      public NUMBER p() { return Distributions.ProbabilityZ(Z()); }

      public NUMBER PooledProportion()
      {
         NUMBER decResult;

         try
         {
            decResult = (N1() * P1() + N2() * P2()) / (N1() + N2());
         }
         catch (Exception e)
         {
            throw new BiostatisticsException(e.Source + ": " + e.Message, e);
         }
         return decResult;
      }

      public NUMBER StandardErrorOfDifference()
      {
         NUMBER decStandardErrorOfDifference;
         try
         {
            decStandardErrorOfDifference = DecMath.Sqrt(PooledProportion() *
               (1.0m - PooledProportion())
               * (1.0m / N1() + 1.0m / N2()));
         }
         catch (Exception e)
         {
            throw new BiostatisticsException(e.Source + ": " + e.Message, e);
         }
         return decStandardErrorOfDifference;
      }

      public NUMBER Z()
      {
         NUMBER decZ;

         try
         {
            if (StandardErrorOfDifference() == 0.0m)
               decZ = Decimal.MaxValue;
            else
               decZ = (DecMath.Abs(Difference()) - 0.5m * ((1.0m / N1()) + (1.0m / N2())))
                  / StandardErrorOfDifference();
         }
         catch (Exception e)
         {
            throw new BiostatisticsException(e.Source + ": " + e.Message, e);
         }

         return decZ;
      }

      #endregion


      private struct Fields
      {
         public Fields(Int32 N1, Int32 N2, NUMBER P1, NUMBER P2)
         {
            if (N1 < 2)
               throw new BiostatisticsException(
                  "N1 value in Fields constructor of ZTest < 2.");
            if (N2 < 2)
               throw new BiostatisticsException(
                  "N2 value in Fields constructor of ZTest < 2."); ;
            if (P1 < 0.0000000000000000000000000001m)
               throw new BiostatisticsException(
"P1 value in Fields constructor of ZTest < minimum positive value of a Decimal.");
            if (P2 < 0.0000000000000000000000000001m)
               throw new BiostatisticsException(
"P2 value in Fields constructor of ZTest < minimum positive value of a Decimal.");

            iN1 = N1;
            iN2 = N2;
            decP1 = P1;
            decP2 = P2;
         }

         public Fields(Fields fields)
         {
            iN1 = fields.iN1;
            iN2 = fields.iN2;
            decP1 = fields.decP1;
            decP2 = fields.decP2;
         }

         public Int32 iN1;
         public Int32 iN2;
         public NUMBER decP1;
         public NUMBER decP2;
      }
   }
}

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