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help for ASH and WARP programs                              (STB-26:  snp6.1)
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Averaged Shifted Histograms and WARPing
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        ^warpstep^

        ^warpoly^

        ^warping^ density midpoint


Description
-----------

These three programs estimate the density of a variable using the WARP
(Weighted Average of Rounded Points) method.  A special case, and the genesis
of the technique is the ASH or Average of Shifted Histograms.  The basic idea
is to average several histograms with different origins to eliminate the
effect of the choice of origin.  By specifying the appropriate weight
function, WARPing can calculate approximate kernel density estimates.  Type
^help kernel^ to see the list of weight functions available.  WARPing is much
more efficient than full kernel density estimation, and the results are
generally indistinguishable.

^warpstep^ displays the WARP estimate in histogram form, while ^warpoly^ displays
the estimate as a frequency polygon.  ^warping^ stores the estimated density
(in ^density^) at selected values of the variable of interest (^midpoint^).

All three of these ado-files call a DOS executable program (^warpings.com^) to
speed the calculations.  ^warpings.com^ reads an ASCII data file in which the
values of the variable of interest are stored in a single column.  Stata's
^outfile^ command can be used to create such a file.  The DOS program is
called by the ado-files and, hence, is invisible to the user.  However, we
have supplied the Pascal source code (^warpings.pas^) to assist readers who
use Stata on non-DOS platforms.  ^warpings.com^ prompts you for the name of
the input data file, the bandwidth of the weight function, the number of
histograms to shift and average, and the weight function.


Examples
--------

The following example displays the ASH for historical data on snowfall.

  . ^warpstep^

 TYPE THE PATH, NAME AND EXTENSION OF TEXT DATA FILE
 ^bufsnow.raw^

 THE NUMBER OF VALUES READ IS:    63

 !!!!!WARNING!!!!!
 IF THIS IS NOT CORRECT PLEASE INTERRUPT AND
 USE STATA COMMAND outfile TO GENERATE AN ASCII
 FILE WITH THE DESIRED DATA VECTOR

 GIVE THE VALUE OF THE BANDWIDTH 'h'
 ^10^

 GIVE THE NUMBER OF HISTOGRAMS TO SHIFT AND AVERAGE
 ^5^          

 SPECIFY THE WEIGHT FUNCTION:

 1 = Uniform; 2 = Triangle(ASH); 3 = Epanechnikov
 4 = Quartic; 5 = Triweight; 6 = Gaussian
 ^2^
 (64 observations read)

 [After a pause for calculations, the graph of the ASH appears.]


Authors
-------

        Isaias H. Salgado-Ugarte, Makoto Shimizu and Toru Taniuchi
        University of Tokyo, Faculty of Agriculture,
        Department of Fisheries, Yayoi 1-1-1, Bunkyo-ku
        Tokyo 113, Japan.
        FAX:    81-3-3812-0529
        EMAIL:  isalgado@@tansei.cc.u-tokyo.ac.jp


Also see
--------

    STB: STB-26 snp6.1, STB-16 snp6
On-line: help for @outfile@, @kernel@ (if installed)