Bioequivalence and Bioavailability Forum

Spreadshit addiction [General Statistics]

posted by yicaoting – NanKing, China, 2011-10-01 18:39 (5018 d 18:54 ago) – Posting: # 7405
Views: 16,330

Dear HS and ElMaestro, thanks for ElMaestro's sharing of that great paper and HS's useful links for R.
To improve the precision of Dr. Russel Lenth's NctInv() in Excel, I have to find a solution to improve the Excel's BetaInv() function instead of direct using of BetaInv() in MS Excel.

I have tested the BetaInv(0.001,2,4) in MS Excel 2007, it returns 0.010101318359375 which is identical to that in Excel 2003. How disappointing with MS's so called improvment. Actually, they did nothing! I will test it in MS Excel 2010 if possible.

I found a solution to improve the precision of Excel's BetaInv() function to a level of MS's so called 10^(-15). It is based on Excel's built-in BetaDist() function which has obviousely higher precision than BetaInv().

'-----------------------------------------------------------------

Public Function NCtInv(p As Double, df As Double) As Double

    Dim X As Double, y As Double, Incr As Double

    If (p <= 0) Or (p >= 1) Or (df <= 0) Then

        MsgBox "Illegal argument", vbCritical, "NCtInv"

        Exit Function

    End If

        If p = 0.5 Then p = 0.5000000001

        If p < 0.5 Then

            'X = Application.BetaInv(1 - 2 * p, 0.5, df / 2)

            X = BetaInverse(1 - 2 * p, 0.5, df / 2)

            NCtInv = -Sqr(df * X / (1 - X))

        Else

            'X = Application.BetaInv(1 - 2 * (1 - p), 0.5, df / 2)

            X = BetaInverse(1 - 2 * (1 - p), 0.5, df / 2)

            NCtInv = Sqr(df * X / (1 - X))

        End If

End Function

'-----------------------------------------------------------------

'-----------------------------------------------------------------

Public Function BetaInverse(p As Variant, Alpha As Variant, Beta As Variant) As Variant

Dim X As Variant

Dim A As Variant

Dim B As Variant

Dim Precision As Variant

X = 0

A = 0

B = 1

Precison = 10 ^ (-15)

Do While B - A > Precision

    X = (A + B) / 2

        If Application.BetaDist(X, Alpha, Beta) > p Then

            B = X

        Else

            A = X

        End If

Loop

BetaInverse = X

End Function

'-----------------------------------------------------------------

How to quickly leave a blank at the head of each row in BEBAC? My code is with blank at several rows, but after I submit the post, the blanks disappeared. ^{*) See note. [HS]}

Using the improved BetaInverse(), I get:
Excel's BetaInv(0.001,2,4)= 0.010101318359375
My BetaInverse(0.001,2,4)= 0.0101017878834719
It can be seen that my BetaInverse(0.001,2,4) is much closer to R's qbeta(0.001,2,4) 0.01010178788373775407572 than Excel's BetaInv(0.001,2,4).

Thus, the new results for ElMaestro's df 5.123 example were refreshed as:

df      p　　　 Excel 2003　　　OO Calc     R

5.123  0.000      #NA          #NA      -Inf

5.123  0.025  -2.55212890  -2.55212890  -2.55212890

5.123  0.500   0.00000006   0.00022634   0

5.123  0.975   2.55212890   2.55212890   2.55212890

5.123  1.000      #NA          #NA       Inf

0.000  0.975      #NA          #NA　    　NaN

Excel's calculation is performed with improved NctInv() containing improved BetaInverse()
Now, the bias has been greatly decreased. May be acceptable in most cases.

Multiple blanks and tabs are removed (that’s the standard behaviour of HTML). If you want to keep multiple blanks highlight the text and click on the Code button right of the text area. Suitable BBCodes will be inserted before/after the text and in HTML rendered in a monospaced font. However, tabs are still removed. For details see here. [Helmut]

Complete thread:

Welch/Satterthwaite in practice ElMaestro 2011-09-21 17:04 [General Statistics]
- Not to round is the question d_labes 2011-09-22 09:11
  - my problem ElMaestro 2011-09-22 12:34
    - Ways out d_labes 2011-09-27 11:54
- Welch/Satterthwaite in practice yicaoting 2011-09-29 16:29
  - Welch/Satterthwaite in practice ElMaestro 2011-09-29 17:39
  - Spreadshit addiction Helmut 2011-09-30 16:52
    - what a divine post! ElMaestro 2011-09-30 18:54
      - what a divine post! Helmut 2011-09-30 19:41
        
        what a divine post! ElMaestro 2011-10-01 13:03
        
        what a divine post! Helmut 2011-10-01 13:20
    - Spreadshit addiction yicaoting 2011-10-01 05:36
      - Spreadshit addiction ElMaestro 2011-10-01 11:13
        
        GNU addiction Helmut 2011-10-02 03:20
      - Spreadshit addiction Helmut 2011-10-01 13:03
        
        Spreadshit addictionyicaoting 2011-10-01 16:39
        Spreadshit addiction yicaoting 2011-10-03 07:23
        
        Spreadshit addiction Helmut 2011-10-03 15:59
        
        Spreadshit addiction yicaoting 2011-10-03 17:35
        
        Spreadshit addiction Helmut 2011-10-03 17:41

Spreadshit addiction [General Sta­tis­tics]

Complete thread:

Spreadshit addiction [General Statistics]