.-
help for ^running^                                              [sed9: STB-24]
.-

Symmetric nearest neighbor smoothing
------------------------------------

    ^running^ yvar [xvar] [^if^ exp] [^in^ range] [^,^ ^d^ouble ^k^nn^(^#^)^ ^nog^raph 

	^gen(^newvar^)^ ^log^it ^m^ean ^r^epeat^(^#^)^ ^sp^an^(^#^)^ graph_options ]


smooths ^yvar^ on ^xvar^. By default the smoothed version is a running line: a
running mean is also available.  A graph of ^yvar^ together with its smooth is
plotted against ^xvar^, unless suppressed. If ^xvar^ is not provided, ^yvar^ is
smoothed against the ordered observations.


Options
-------

^double^ doubles the value of ^repeat^.  If ^repeat^ is not specified, ^double^ is
    equivalent to ^repeat(2)^. 

^gen(^newvar^)^ creates ^newvar^ containing the smoothed values of ^yvar^.  Note that
    ^newvar^ will be on a logit scale if ^logit^ is used.

^nograph^ suppresses the graph. 

^knn(^#^)^ controls the number of nearest neighbors used on each side of the
    smoothed point.  The value of ^knn^ is stored in S_1. The greater the value,
    the greater the smoothing. If ^span^ is specified ^knn^ is ignored.  

^logit^ transforms the smooth and plots the y-axis on a logit scale.  The
    observations are automatically jittered in the vertical scale and are
    plotted just above and outside the range of the smoothed curve.

^mean^ specifies running-mean least-squares smoothing; default is running-line.

^repeat(^#^)^ specifies the number of times the data are to be smoothed. The
    default is 1.  Increasing ^repeat^ increases the time it takes to calculate
    the smooth but improves the smooth.  However, you may need to increase the
    bandwidth to obtain the same degree of smoothness.

^span(^#^)^ controls the span or proportion of the data to be used in the symmetric
    nearest neighbors. If ^span^ is specified, ^knn^ is defined to be (N*^span^-1)/2,
    where N is the number of observations. If both ^span^ and ^knn^ are specified,
    ^knn^ is ignored.  Stored in S_2.

graph_options are any of the options allowed with ^graph, twoway^; see ^help^
    ^graph^.  Graph plots ^yvar^ followed by its smooth against ^xvar^, the default
    options are s(oi) and c(.l).


Remarks
-------

Subsets of (2*k+1) observations are used for calculating smoothed values for
each point in the data except for end points, for which smaller uncentered
subsets are used.  The subsets consist of the closest k points with ^xvar^ values
less than or equal to that of the given point, the point itself, and the
closest k points with ^xvar^ values greater than or equal to the given point.

Since the neighborhoods are asymmetric in the tails, the running-mean is
subject to bias in the tails.  For this reason the smooth is set to missing in
the tails if ^mean^ is specified.  Other than in the tails, using ^mean^ will
produce the same result as using the default smooth whenever the ^xvar^ values
are evenly spaced.  ^repeat(^3^)^, for instance, first smooths ^yvar^ creating yhat1,
say; next yhat1 is smoothed creating yhat2, and finally yhat2 is smoothed
creating yhat3.  


Author
------

        Peter Sasieni
        Imperial Cancer Research Fund, London
        FAX 011-44-171-269-3429


Also see
--------

 Manual:  [5s] ksm, [5s] smooth
    STB:  sed9 (STB-23)
On-line:  ^help^ for @ksm@ and @smooth@