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help for ^running^                                           (STB-41: sed9.1)
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Symmetric nearest neighbor smoothing 
-------------------------------------

    ^running^ yvar [xvar] [^if^ exp] [^in^ range] [weight] [^,^ ^ci^ ^d^ouble ^gen(^newvar^)^ 
	^gense(^sevar^)^ ^genb(^bvar^)^ ^k^nn^(^# | knnvar^)^ ^log^it ^m^ean ^nog^raph ^r^epeat^(^#^)^
	^sp^an^(^#^)^ ^tw^ice graph_options ]


^running^ 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.

Only analytic weights (^aweight^) are allowed; see help @weights@.


Options
-------

^ci^ produces a pointwise confidence interval for the smoothed values of yvar.
    The width is determined by the current value of the macro $^S_level^. Not 
    available with ^twice^, ^repeat^ or ^logit^.

^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.

^gense(^sevar^)^ creates sevar containing the pointwise standard error of
    smoothed values of yvar.  Not available with ^twice^, ^repeat^ or ^logit^.

^genb(^bvar^)^ creates bvar containing the local slope estimates. They 
    constitute a local estimate of the derivative of the smoothed values of
    yvar with respect to xvar. Not available with ^mean^, ^twice^  or ^logit^.

^nograph^ suppresses the graph. 

^knn(^# | knnvar^)^ controls the number (K) of Nearest Neighbors used on each side
    of the smoothed point. You may specify a constant (#) or a variable
    (knnvar). The value # is stored in $^S_1^. The greater the value, the greater
    the smoothing. You are not allowed to specify both ^span()^ and ^knn()^.

^logit^ transforms the smooth and plots the y-axis on a logit scale.  Zero-one
    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.  ^repeat(2)^ corresponds to "smoothing
    the smooth".

^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,
    an error results.  ^span^ must be be in the range (0,2]. (It must be less
    than 1 when using ^mean^.)  Span 2 corresponds to fitting a straight line.  
    Stored in $^S_2^.

^twice^ carries out Tukey's `twicing' procedure whereby residuals from the
    original fit are smoothed and added back to the fit to obtain the final
    smooth ("smoothing the rough" or "reroughing" in Tukey's terminology). The 
    result is somewhat rougher than would have been obtained without the 
    application of twicing, but may be a better fit to the data.

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(oiii) (or s(.iii) with over 299 observations), c(.lll) and
    p(23) (or p(2344) when ^ci^ is specified).


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 44-171-269-3429

	Patrick Royston
        Royal Postgraduate Medical School, London
        FAX 44-181-383-8573


Also see
--------

    STB:  STB-41 sed9.1, STB-24 sed9
 Manual:  [R] ksm, [R] smooth
On-line:  help for @ksm@ and @smooth@