This article shows you how to create a Visual Basic for Applications
procedure to open a table, read the data, and find the statistical
median. The median is a measure of central tendency, another "middle" measurement of a data set, like the mean or average). The data set consisting of the numbers 1, 2, 3, 6, and 100 has a median of 3, the middle of the set. The data set consisting of the numbers 1, 2, 6, and 10 has a median of 4, the middle of the set [(2 + 6) / 2 = 4].
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. However, 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 correctly, 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:
- Create a module and type the following line in the Declarations
section:
Option Explicit
- 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
If Not ssMedian Is Nothing Then
ssMedian.Close
Set ssMedian = Nothing
End If
Set MedianDB = Nothing
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