#!/usr/bin/perl -w

# file to ,  leans heavily on:
## $Header: /cys/people/brenner/http/docs/web/perl5/RCS/simple-form.cgi,v 1.5 1996/03/29 22:58:40 brenner Exp $
## Copyright (C) 1994 Steven E. Brenner
# this file was written by Chris Evans (http://www.psyctc.org/cgi-bin/mailto.pl?webmaster) 
# and, though it's trivial, I claim copyright on it
# However, you may copy it freely provided:
# 1) you don't make a profit out of copying it or using it
# 2) or if you do, you liaise with me about it and we strike a deal!!
# 3) you don't change it any way (particularly not removing this stuff!)
# 4) or if you do change it, you liaise with me, and, with suitable credit
#    to you, we improve the original in line with what you've done!
# The correct citation for this file is:
# Evans (1998) rcsc1.prl http://www.psyctc.org/stats/rcsc1.prl
# 24.v.98

require 5.001;
use strict;
require "/usr/lib/cgi-bin/cgi-lib.pl";

MAIN:
{
  my (%input,    # The CGI data then the following are munged
      $rel,
      $sd,
      $data_there,
      $se_change,
      $rc_crit,
      $width,
      $dp,
      $field,
      $high_start,
      $low_start,
      $high_start_end_rel,
      $high_start_end_rel_drop,
      $high_start_end_not_rel,
      $low_start_end_not_rel,
      $low_start_end_rel);   # Each of the fields (used for testing) 
  

  # $width and $dp set the output format
  $width = 8;
  $dp = 2;
  # Read in all the variables set by the form
  &ReadParse(\%input);

  # Check that what's needed has been entered
  $data_there = 1;
  foreach $field (qw(rel sd)) {
    $data_there = 0 if !(length($input{$field}));
  }
  &CgiDie("Error: data missing\n") unless $data_there;

  # Print the header
  print &PrintHeader;
  print &HtmlTop ("Reliable change");
  print "</CENTER>\n";

  # get the data into variables
  $rel = $input{'rel'};
  $sd = $input{'sd'};

  # now process the data acquired
  if (!($rel =~ /[\d\.]/)) { 
     &CgiDie("Reliability as read from your input = $rel\n<P>Reliability MUST be a number.  Try again!\n");
  }
  if ($rel <= 0) {
     &CgiDie("Reliability as read from your input = $rel\n<P>Reliability MUST be more than zero.  Try again!\n");
  }
  if ($rel > 1) {
     &CgiDie("Reliability as read from your input = $rel\n<P>Reliability MUST be less (or, implausibly, equal to) 1.  Try again!\n");
  }
  if ($rel == 1) {
     print "WARNING: Reliability as read from your input = $rel\n<BR>Perfect reliability is highly implausible.<P>\n";
  }
  if ($rel <= .5) {
     print "WARNING: Reliability as read from your input = $rel\n<BR>That's rather poor reliability!\n<P>\n";
  }


  if (!$sd =~ /[\d\.]/) { 
     &CgiDie("s.d. as read from your input = $sd\n<P>s.d. MUST be a number.  Try again!\n");
  }
  if ($sd <= 0) {
     &CgiDie("s.d. as read from your input = $sd\n<P>s.d. MUST be more than zero.  Try again!\n");
  }
  
  # calculate reliable change criterion
  $se_change = $sd*(sqrt(2))*sqrt(1-$rel);
  $rc_crit = 1.96*$se_change;
  print "<b><i>You entered: Reliability = $rel\n s.d. = $sd</i><BR>";
  printf "The standard error of change given these values is %${width}.${dp}f <BR>\n",$se_change;
  printf "The reliable change criterion (RC, RCrit or RCCrit) is 1.96 times this, i.e. %${width}.${dp}f <BR>\n",$rc_crit;
  print "Change, up or down, greater than this should be regarded as reliable.</b>";
  $high_start = 1.4*$rc_crit;
  $low_start = 0.8*$rc_crit;
  $high_start_end_rel = 0.2*$rc_crit;
  $high_start_end_rel_drop = $high_start - $high_start_end_rel;
  $high_start_end_not_rel = 0.7*$rc_crit;
  $low_start_end_not_rel = 0;
  $low_start_end_rel = 0 - 0.7*$rc_crit;
  $width = 4;
  $dp = 2;
  printf "<p>For example, if you had a client with a starting score on the change measure of %${width}.${dp}f",$high_start;
  printf " and his or her end score was %${width}.${dp}f",$high_start_end_rel;
  print " then that was reliable change because there";
  printf "was a drop of %${width}.${dp}f",$high_start_end_rel_drop;
  printf " which is greater than reliable change criterion you calculated of %${width}.${dp}f",$rc_crit;
  print " That means that this was a reliable improvement (assuming that a drop in score is an improvement!)";
  print " I.e. it is a change in that direction that would be expected less than 2.5% of the time if the";
  print " only source of change were unreliability of measurement.";

  printf "<p> <p>By contrast, someone starting from the same score who ended up on %${width}.${dp}f",$high_start_end_not_rel;
  printf " would not have achieved reliable improvement as the drop is less than %${width}.${dp}f",$rc_crit;

  printf "<p> <p>To give another example, someone starting on %${width}.${dp}f",$low_start;
  printf " who drops to %${width}.${dp}f",$low_start_end_not_rel;
  printf " cannot have achieved reliable improvement as again, that change is not more than %${width}.${dp}f",$rc_crit;
  printf " However, had they dropped (if the scale allows it) to %${width}.${dp}f",$low_start_end_rel;
  printf " then clearly they have dropped by more than %${width}.${dp}f",$rc_crit;
  print " and so they have shown a reliable improvement.";

  print "<p> <p>All the same applies for people whose scores deteriorate, i.e.";
  print " get higher in the example of a problem scored measure that I'm using.<br>";
  printf "  Here again, changes more than %${width}.${dp}f",$rc_crit;
  print " are reliable change but those changes are reliable deteriorations not improvements.";

   print "\n<HR>\n<UL>\n";
   print "<LI><A HREF=\"http://www.psyctc.org/stats/\">other statistical info. at this site</A>\n";
   print "<LI><A HREF=\"http://www.psyctc.org/stats/rcsc.htm\">reliable and clinical change info.</A>\n";
   print "<LI><A HREF=\"http://www.psyctc.org/tools/\">tools and measures page</A>\n";
   print "<LI><A HREF=\"http://www.psyctc.org/grids/\">grids and PCP pages</A>\n";
   print "<LI><A HREF=\"http://www.psyctc.org/\">main site intro. page</A>\n</UL>";
   # Close the document cleanly.
   print &HtmlBot;


}