-----SHIFT PLOT--------------------------------------
 
SHIFT PLOT
 
Name:
    SHIFT PLOT
 
Type:
    Graphics Command
 
Purpose:
    Generates a shift plot.
 
Description:
    The shift plot is a plot of

        y(q) - x(q) versus x(q)

    with y(q) and x(q) denoting the qth quantiles of y and x,
    respectively.  Although this plot can be generated for any
    pair of variables, the primary usage of this plot is for the
    case where x is a control group and y is an experimental
    method.  Alternatively, x could represent an "old" method
    while y represents a "new" method.  The plot measures how much
    the control group must be shifted so that it is comparable to
    the expermimental method (relative to the quantiles).

    The quantiles of a distribution are the distribution's "percent
    points" (e.g., the 0.5 quantile = 50% point = median).

    The plot consists of the following:
       Vertical axis   = difference in the estimated quantiles
                         between data set 1 and data set 2;
       Horizontal axis = estimated quantiles from data set 2.

    The shift plot is a variation of the quantile-quantile plot
    and the Tukey mean-difference plot.

Syntax 1:
    SHIFT PLOT <y> <x>      <SUBSET/EXCEPT/FOR qualification>
    where <y> is the response variable for the experimental group;
          <x> is the response variable for the control group;
    and where the <SUBSET/EXCEPT/FOR qualification> is optional.
 
    With this syntax, the quantiles correspond to the data points
    of the <x> variable.

Syntax 2:
    SHIFT PLOT <y> <x> <q>     <SUBSET/EXCEPT/FOR qualification>
    where <y> is the response variable for the experimental group;
          <x> is the response variable for the control group;
          <q> is a variable containing values between 0 and 1 that
              specifies the desired quantiles to plot;
    and where the <SUBSET/EXCEPT/FOR qualification> is optional.
 
    With this syntax, you explicitly give the desired quantiles.

Examples:
    SHIFT PLOT Y X
    SHIFT PLOT Y X  SUBSET X > 1
    SHIFT PLOT Y X XQ
    SHIFT PLOT Y X  XQ SUBSET X > 1
 
Default:
    None
 
Synonyms:
    None
 
Related Commands:
    CHARACTERS                 = Sets the type for plot characters.
    LINES                      = Sets the type for plot lines.
    QUANTILE-QUANTILE PLOT     = Generates a q-q plot.
    TUKEY MEAN-DIFFERENCE PLOT = Generates a Tukey mean-difference plot.
    BIHISTOGRAM                = Generates a bihistogram.
    T-TEST                     = Carries out a 2-sample t test.
    F-TEST                     = Carries out a 2-sample F test.
 
Reference:
    "Introduction to Robust Estimation and Hypothesis Testing",
    Rand R. Wilcox, Academic Press, 1997.
 
Applications:
    Exploratory Data Analysis
 
Implementation Date:
    2003/2
 
Program:
    SKIP 25
    READ AUTO83B.DAT Y1 Y2
    .
    DELETE Y2 SUBSET Y2 < 0
    LABEL CASE ASIS
    Y1LABEL Difference between Y1 and Y2 Quantiles
    X1LABEL Quantiles for Y2
    CHARACTER X
    LINE BLANK
    SHIFT PLOT Y1 Y2