Adjusted Natural Cubic  Spline					[snp7: STB-22]
------------------------------

   ^sp_adj^ yvar xvar [[^if^ exp] [^in^ range] [^, n^knots^(^#^)^ ^kn^ots^(^#,...,#^)^
	^a^djust^(^varlist^)^ ^reg^ress^(^string^)^ ^gen(^newvar^)^ ^nog^raph graph_options ]


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

^sp_adj^ fits a natural cubic spline in xvar to yvar adjusting for the
variables in ^adjust^ and, by default, plots the fitted smooth curve.  
The regression can be carried out with any ^estimate^ command, the default 
being ^regress^ (ordinary least squares).  ^sp_adj^ optionally saves the 
adjusted smooth transformation.  



Options
-------

^knots^ specifies the exact location of the interior knots.

^nknots^ specifies the number of interior knots. (Ignored if the locations
	are specified).

^regress(^estimate^)^ fits the cubic spline using the command "estimate".
	The default is ^regress^. If ^cox^ is used, the censoring variable
	may be specified using ^dead^. Similarly the option ^strata^ may be
	used with ^clogit^.  If using ^blogit^, ^bprobit^, ^glogit^, or 
	^gprobit^, put the pop_var as the first varaible in ^adjust^.

^adjust^ provides a list of additional variables to be included in the 
	regression. If using logit or probit with grouped data, the first
	varaible in ^adjust^ should be the pop_var.

^nograph^ suppresses the graph. 

^gen(^newvar^)^ creates newvar containing the smooth transformation of yvar.
	The variable is in the scale of the linear predictor (index) in the
	chosen regression model.

graph_options are any of the options allowed with ^graph, twoway^; see 
    ^help graph^.


Remarks
-------

The natural cubic spline has knots at the ends of xvar as well at the interior
sites.  It is constrained to be linear beyond the the extreme knots and to be
everywhere twice continuously differentiable.  By default the interior knots
are placed at equally spaced quantiles.


Author
------

        Peter Sasieni
        Imperial Cancer Research Fund, London
        FAX 011-44-71-269-3429


Also see
--------

 Manual:  [4] estimate
    STB:  snp7 (STB-22)
On-line:  ^help^ for ^graph^, ^spline^, and ^spbase^