Delila Program: multtest

multtest program

Documentation for the multtest program is below, with links to related programs in the "see also" section.

{   version = 1.21; (* of multtest.p 2007 Mar 21}

(* begin module describe.multtest *)
   multtest: multiple Student's t-test

   multtest(distributions: in, multtestp: in,
            list: out, xyin: out, key: out, output: out)


   distributions:  parameters to control the program:
      A set of 3 numbers on one line defines a distribution:
         N                   (integer)
         mean                (real)
         standard deviation  (real)

      This file contains a series of such distributions, one per line.

      fudgefactor: If a line begins with 'f' then all standard deviations
      from that point on (until the next 'f') will be multiplied by the
      number following on the same line as f.  This allows one to see the
      effects if the standard deviation does not account for all

      Lines that begin with '*' are comments.

   multtestp:  a single character OR pairs of numbers, one per line, that
      represent the distributions to be compared by a ttest.  The
      distributions listed are the only ones output to the list file.

      controlchar:  If a line begins with a character then:
         l: compute the natural log of the mean and adjust the standard
            deviation accordingly (divide by the mean).

         c: set the color transform.  The next character is the colortype:
            the colors produced in xyin are adjusted:

            n: normal colors
               Hue is set to the probability.

            i: interval colors.  The 'i' must be followed by the number
               of intervals to truncate the colors to.
               Hue is set to the truncated probability.
               For example, if the number of intervals is 2, then the colors
               will be 0.0 to 0.5 and 0.5 to 1.

            s: standard interval colors.
               The colors will cut off at the points 0.50, 0.90 to 0.95 and

   list:  Input values, calculated Student's t value and probabilities that
     the numbers are the same, along with the Z score for the energy
     deviation from zero, and the probability that this deltadeltaG is zero.
     The pairs to be listed are defined in the multtestp file.

   xyin:  input to xyplo program:
     column 1: (integer) first distribution number
     column 2: (integer) second distribution number
     column 3: (integer) hue fraction
     column 4: (integer) saturation fraction = 1
     column 5: (integer) brightness fraction = 1

     The hue is computed from the probability according to the colortype
     defined in multtestp.

   key:  input to xyplo program, same colomuns but generates the key
     for the probabilities.

   output: messages to the user


   This program performs T test computations for pairs of distributions and
   converts them to probabilities that the means are the same.  This is a
   two-tailed Student's t test.


   For a multtestp file:

1 2

   with a distributions file:

3 118 36
3 205 26

   The resulting list file is:

multtest 1.02
              distribution 1 | distribution 2
number                     3 |              3
mean               118.00000 |      205.00000
standard dev.       36.00000 |       26.00000
sigma-D =       25.63851
degrees of freedom = 4
t =        3.39333
p(1=2) =        0.02745
This is the probability that they are the same.


author = "W. H. Press
 and B. P. Flannery
 and S. A. Teukolsky
 and W. T. Vetterling",
title = "Numerical Recipies in Pascal.
The Art of Scientific Computing",
publisher = "Cambridge University Press",
address = "Cambridge",
year = "1989"}

Given a t value from a Student's t test, and the degrees of freedom, df,
return the probability for a two tailed test.  The code for doing this was
originally in java script, from:

Richard Lowry
Department of Psychology
Vassar College
Poughkeepsie, NY  12604-0396  USA
office:  (914)437-7381
fax:  (914)437-7538

The original functional html containing this code is also given.
It was translated to Pascal by Tom Schneider.

see also
   The source program: ttest.p

   The xyin file can be graphed using:

   Results can be checked at:

   The method of conversion to a log scale comes: calc.p

   Thomas Dana Schneider


technical notes

(* end module describe.multtest *)
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