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<title>ploticus: proc pvalue</title>
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  <td><br><h2>proc pvalue</h2></td>
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  <small>
  <a href="../doc/welcome.html"><img src="../doc/ploticus.gif" border=0></a><br>
  Version 2.41 Mar2009
     </small><br><a href="../doc/scripthome.html">Scripts</a>
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.TH proc_pvalue PL "11-MAR-2009   PL ploticus.sourceforge.net"

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<center>
<a href="../gallery/pvalue1.htm">
<img src="../gallery/pvalue1_chunk.gif">
</a>
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\fBproc pvalue\fR computes and displays p values associated with a statistical t test (New in version 2.41).
A t test compares two groups of numeric scores; the associated p value is the probability 
that there is no significant difference between group1 and group2.
A low p value (typically < 0.05 or < 0.01) indicates that there's a sufficiently significant 
difference between group1 and group2.  This is useful for example, in treatment vs. control studies
in being able to say that the treatment made a difference or not.
.LP
How your data must be organized:
Each data row must have fields for mean, SD, and N, for group1 and group2,
plus a X category identifier field (total of 7 fields required).
The mean, SD and N can be computed from raw data using proc processdata (action=summary),
and then joined (using proc processdata again, action=join) so that data for both groups are together on each row.
See the above example which uses this technique.
.LP
This proc will compute one p value per data row, and display it at the X category location matching
the group identifier field  (so X scaletype must be categories).  By default the p value will be displayed 
using the format eg. "p=0.12", along the bottom of the plot area, and
statistically significant p values are highlighted in yellow.
.LP


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<br><br><br>
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.SH Attributes
\fCxfield\fR, \fCstatfields1\fR, and \fCstatfields2\fR \fBmust\fR be specified.

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<br><br>
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.LP
\fBxfield\fR
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&nbsp; &nbsp;
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<a href="attributetypes.html#dfield">
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\0dfield
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</a>
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.IP \0
Data field containing an identifier for determining where in X the p value will be displayed.

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<br><br><br>
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.LP
\fBstatfields1\fR
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&nbsp; &nbsp;
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<a href="attributetypes.html#dfield">
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\0meanfield
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</a>
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<a href="attributetypes.html#dfield">
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\0SDfield
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</a>
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<a href="attributetypes.html#dfield">
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\0Nfield
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</a>
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.IP \0
Three data fields containing mean, SD, and N for group1.

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<br><br><br>
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.LP
\fBstatfields2\fR
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&nbsp; &nbsp;
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<a href="attributetypes.html#dfield">
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\0meanfield
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</a>
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<a href="attributetypes.html#dfield">
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\0SDfield
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</a>
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<a href="attributetypes.html#dfield">
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\0Ndfield
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</a>
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.IP \0
Three data fields containing mean, SD, and N for group2.

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<br><br><br>
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.LP
\fBtextdetails\fR
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&nbsp; &nbsp;
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<a href="textdetails.html">
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\0textdetails
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</a>
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.IP \0
Size, color, etc. of the p value string.
This attribute can also be used to adjust the location of the displayed string.
.br
Example: \fCtextdetails: size=7 adjust=0,-0.25\fR

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<br><br><br>
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.LP
\fBprintformat\fR
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&nbsp; &nbsp;
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string
.IP \0
Controls formatting of the result string and the pvalue numeric. Default is \fCp=%2.2f\fR.
.br
Example: \fCprintformat: p = %3.3f\fR

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<br><br><br>
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.LP
\fBlowp\fR
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&nbsp; &nbsp;
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h
.IP \0
Mathematically, p values can never reach absolute 0.
Convention holds that p values less than a certain threshold be displayed as eg. \fCp < 0.01\fR
This attribute controls that threshold.  Default is 0.01
.br
Example: \fClowp: 0.005\fR

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<br><br><br>
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.LP
\fBsignif\fR
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&nbsp; &nbsp;
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h
.IP \0
Convention holds that p values less than a certain threshold indicate a 
sufficiently significant difference between the two groups.
By default this proc highlights these in yellow.
Default is 0.05.
.br
Example: \fCsignif: 0.01\fR

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<br><br><br>
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.LP
\fBsignifcolor\fR
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&nbsp; &nbsp;
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<a href="color.html">
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\0color
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</a>
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 | \fCnone\fR
.IP \0
The color to use when highlighting "significant" p values.  Default is yellow.
To turn off the highlighting feature specify \fCnone\fR.

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<br><br><br>
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.LP
\fBselect\fR  
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&nbsp; &nbsp;
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<a href="select.html">
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\0select expression
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</a>
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.IP \0
Allows data rows to be selected for inclusion using a selection expression.
.br
Example: \fC@@2 = B\fR

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<br><br><br>
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