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help for ^xtmod^            (Version 0.9 20 February 2009)
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Analyze and display interactions based on time-series data
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        ^xtmod^ @varlist@ [if] [in] [, Controlvariables(@varlist@) Regopts(string) 
	ARROWOFFset(#.#) ARROWXLENgth(#.#) ARROWYLENgth(#.#) PRECision(#.#) 
	GLS NOCONStant MAX Tests]

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

	^xtmod^ helps running multiple moderated regressions. It generates the 
	necessary interaction variables, calculates the coefficients, optionally 
	displays tests, and displays the interaction. It is mainly a convenience 
	script that instrumentalizes individually available commands such as xtgls. 

	Warning: The program has not been tested with categorical variables. Please 
	notify the author of bugs.


Options
-------

	^controlvariables^(@varlist@) specifies control variables to be included in 
	the regression
	
	^regopts(string)^ allows the user to pass options to the regression command, 
	e.g., panels(heteroskedastic) in the case of xtgls

	^arrowoffset(#.#)^ specifies how much the arrow head is offset from the 
	left-most point of the regression line. Ranges from 0.0 to 1.0 

	^arrowxlength(#.#)^ specifies how much the equation text is offset to the 
	right from the arrow's head. Ranges from 0.0 to 1.0 

	^arrowxlength(#.#)^ specifies how much the equation text is vertically offset 
	from the arrow's head. Ranges from 0.0 to 1.0 
	
	^precision(#.#)^ specifies the precision used to display numbers in the graphic

	^gls^ tells ^xtmod^ to run ^xtgls^ instead of ^xtreg^

	^noconstant^ tells ^xtmod^ that the constant equals zero. Can only be used 
	when gls has been specified
	
	^max^ tells ^xtmod^ to plot the graphic using the minimum and maximum values 
	of the moderator as opposed to mean +/- standard deviation values (the default)

	^tests^ instructs ^xtmod^ to run post-hoc tests on simple slope differences 
	(compare Aiken and West, 1991)


Examples
--------

        . ^xtmod roa apcogs salesdiff rf, d(leverage industry?) r(panels(hetero)) arrowylen(0.9) gls nocons tests^
        . ^xtmod lndroa C_lnapcogs C_sales, tests^

References
----------

	Aiken, L.S. and S.G. West. "Multiple Regression: Testing and Interpreting Interactions. 
	1991. Thousand Oaks: Sage Publications.

	Stata FAQ, How can I understand a continuous by continuous interaction? UCLA: 
	Academic Technology Services, Statistical Consulting Group. 
	from http://www.ats.ucla.edu/stat/stata/faq/concon.htm (accessed February 20, 2009).

	Stata FAQ, Part 1: How can I understand a 3-way continuous interaction? UCLA: 
	Academic Technology Services, Statistical Consulting Group. 
	from http://www.ats.ucla.edu/stat/stata/faq/con3way.htm (accessed February 20, 2009).

Author
------

        Daniel Seifert, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
        daniel.seifert@@epfl.ch

Also see
--------

 Manual:  ^[R] xtreg^, ^[R] xtgls^, ^[G] schemes intro^
On-line:  help for @xtreg@, @xtgls@, @schemes@