ACC2000: How to Use Code to Derive a Statistical Median (210581)

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Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. NOTE: The sample code in this article uses Microsoft Data Access Objects. For this code to run properly, you must reference the Microsoft DAO 3.6 Object Library. To do so, click References on the Tools menu in the Visual Basic Editor, and make sure that the Microsoft DAO 3.6 Object Library check box is selected.

To create a procedure that determines the statistical median of a set of numbers, follow these steps:

1. Create a module and type the following line in the Declarations section:

   Option Explicit

2. Type or paste the following procedure:

   Function Median (tName As String, fldName As String) As Single
     Dim MedianDB As DAO.Database
     Dim ssMedian As DAO.Recordset
     Dim RCount As Integer, i As Integer, x As Double, y As Double, _
         OffSet As Integer
     Set MedianDB = CurrentDB()
     Set ssMedian = MedianDB.Openrecordset("SELECT [" & fldName & _
               "] FROM [" & tName & "] WHERE [" & fldName & _ 
               "] IS NOT NULL ORDER BY [" & fldName  & "];")
     'NOTE: To include nulls when calculating the median value, omit
     'WHERE [" & fldName & "] IS NOT NULL from the example.
     ssMedian.MoveLast
     RCount% = ssMedian.RecordCount
     x = RCount Mod 2
     If x <> 0 Then
        OffSet = ((RCount + 1) / 2) - 2
        For i% = 0 To OffSet
           ssMedian.MovePrevious
        Next i
        Median = ssMedian(fldName)
     Else
        OffSet = (RCount / 2) - 2
        For i = 0 To OffSet
           ssMedian.MovePrevious
        Next i
        x = ssMedian(fldName)
        ssMedian.MovePrevious
        y = ssMedian(fldName)
        Median = (x + y) / 2
     End If
     ssMedian.Close
     MedianDB.Close
   End Function
   					

How to Use the Median() Function

Create a form and add a text box control where you want to display the median values of a data set. Set the ControlSource property of the text box control to the following:

=Median("<TableName>", "<FieldName>")
				

The value of this control is the median of the data set. Another way to use this function is to call it from within another function that compares the median from different data sets. For example:

   Function CompareMedians()
      Dim MyDB as Database
      .
      .
      .
      X = Median("<TableName>", "<FieldName>")
      Y = Median("<TableName>", "<FieldName>")
      If X > Y Then Debug.Print "The median for X is greatest."
   End Function