overlay several graphs
-----------------------

^overlay^ , ^by(^varlist^)^  ^xlab(^numlist^)^ ^ylab(^numlist^)^ ^function(^string^)^ 
   ^saving(^filename^)^ ^graph_options^

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

This function draws several graphs in one area of the graphics window. As a result this
function is very versatile and will work well with any graph function that allows
the user to specify the axes. The function will, by default,  
try and calculate an axes that remains unchanged for each graph, this may fail and the
user then has to specify the axes using ^xlab^ and ^ylab^.

Any options for the graphing function can be added to the end of the command line. 
This can be options like the plotting symbol and connecting points.

WARNING: to get the same scales make sure you specify the
xlab and ylab options and hence this should fix the axes.

Options
-------

^by(^varlist^)^  specifies the strata for the multiple graphs.

^saving(^filename^)^ saves the graph as filename.gph.

^function(^string^)^ specifies the command that draws the graph. If this
is not specified then the {\tt graph} function is used.

^xlab(^numlist^)^ specifies axes labels.

^ylab(^numlist^)^ specifies axes labels.

Examples
--------


.overlay pef day0, by(patient) c(l) s(.) sort saving(graph1)


.overlay pef if patient<5028, by(patient) function(kdensity) xlab(150,350,680) 
ylab(0,0.02, 0.045) s(.) saving(graph3)

.overlay pef if patient<5028, by(patient) xlab(150,350,680) bin(8) ylab(0,1.1)

If the user wants to have fitted lines from a regression with confidence interavals 
for several subgroups

.overlay yhat yhatupper yhatlower x, by(subgroups) c(ll[-]l[-].) s(iiio)

Author
------
   Adrian Mander
   GSK, Harlow UK.
   adrian.p.mander@gsk.com

Also see
--------

 Manual:  ^[R] kdensity^
On-line:  help for @kdensity@, @graph@