{smcl}
{* *! version 3.0 20march2010}{...}
{cmd:help spundir}
{hline}

{title:Title}

{title:spundir - Creates {it}undirected dyad{bf} contagion spatial effect variable}


{title:Syntax}

{p 8 17 2}
{cmdab:spundir}
lagvar {ifin}, {opt w:eightvar(varname)} {opt i(varname)} {opt j(varname)} {opt link(options)}
 [{cmd:}{it:options}]

{synoptset 20 tabbed}{...}
{synopthdr}
{synoptline}
{synopt:{opt time(varname)}}contains the numeric time variable{p_end}
{synopt:{opt excl:usive}}exclusive undirected dyad contagion{p_end}
{synopt:{opt nor:owst}}spatial effect variable not row-standardized{p_end}
{synopt:{opt nom:erge}}no automatic merge of spatial effect variable into original dataset{p_end}
{synopt:{opt se:name(name)}}name to be given to created spatial effect variable{p_end}
{synopt:{opt label:name(name)}}name of label given to spatial effect variable{p_end}
{synopt:{opt file:name(name)}}name of file to which spatial effect variable saved{p_end}
{synoptline}
{p2colreset}{...}


{title:Description}

{pstd}
{cmd: spundir} generates an undirected dyad contagion spatial effect variable for analysis of spatial dependence in undirected dyad data.
It can create spatial effect variables for spatial lag, spatial-x and spatial error models.
See Neumayer and Plümper (2010) for an exposition of all possible forms of contagion in dyadic data.
See Plümper and Neumayer (2010) for a discussion of model specification in the analysis of spatial dependence.

{title:Additional information}

{pstd}
See {browse "http://personal.lse.ac.uk/neumayer/spundir.htm"}.

{title:Arguments}

{phang}
{opt lagvar} is the variable to be spatially lagged. It is the undirected dyadic dependent variable in spatial lag models, a selected independent
variable in spatial-x models and a saved regression residual in spatial error models.

{phang}
{opt w:eightvar(varname)} is the weighting or connectivity variable linking unit {it}i{sf} with unit {it}j{sf}. It must be numeric
and must not contain negative values. It may or may not be directed.

{phang}
{opt i(varname)} is the identifying variable of unit {it}i{sf}. It can be a numeric or string variable.

{phang}
{opt j(varname)} is the identifying variable of unit {it}j{sf}. It can be a numeric or string variable.


{title:Options}

{phang}
{opt link(options)} is required. The following options are allowed:
{it}ik{sf}, {it}ki{sf}, {it}jm{sf}, {it}mj{sf}, {it}ik+jm{sf}, {it}ki+mj{sf},
{it}ik*jm{sf}, and {it}ki*mj{sf}.
Option {it}ik{sf} requests that the virtually transformed weighting variable {opt w:eightvar(varname)} is to represent connectivity from unit {it}i{sf}
to other units {it}k{sf}. Option {it}ki{sf} requests connectivity from other units {it}k{sf} to unit {it}i{sf}. 
Option {it}jm{sf} requests connectivity from unit {it}j{sf} to other units {it}m{sf}. 
Option {it}mj{sf} requests connectivity from other units {it}m{sf} to unit {it}j{sf}. 
Option {it}ik+jm{sf} requests that the weighting matrix represents the {it}sum{sf} of connectivities invoked by {it}ik{sf} and {it}jm{sf}.
Option {it}ki+mj{sf} does the same, but for the sum of connectivities invoked by {it}ki{sf} and {it}mj{sf}. 
Option {it}ik*jm{sf} requests that the weighting matrix represents the {it}product{sf} of connectivities invoked by {it}ik{sf} and {it}jm{sf}.
Option {it}ki*mj{sf} does the same, but for the product of connectivities invoked by {it}ki{sf} and {it}mj{sf}. 

{phang}
{opt time(varname)} is an optional argument. If users wish to generate a time-varying spatial effect variable, then the numeric time variable must be stated here.

{phang}
{opt excl:usive} specifies that all dyads containing either unit {it}i{sf} or unit {it}j{sf} are excluded from having a spatial
effect on dyad {it}ij{sf}.

{phang}
{opt nor:owst} requests that the generated spatial effect variable is not row-standardized.
See Plümper and Neumayer (2010) for an explanation and discussion of row-standardization.
Row-standardization is the default option.

{phang}
{opt nom:erge} requests that the generated spatial effect variable is not automatically merged into the original data set.

{phang}
{opt se:name(name)} names the generated spatial effect variable. In the default option,
if the weighting matrix is row-standardized, then the generated spatial effect variable is called SE_var_undirdyad_rowst. If the weighting matrix
is not row-standardized, then a file is saved in the current working directory called SE_var_undirdyad_norowst. 
Any previously existing variable with the same name will be replaced.

{phang}
{opt label:name(name)} names the label of the generated spatial effect variable. The default label given is
"Undirected dyad contagion spatial effect variable".

{phang}
{opt file:name(name)} requests that a dataset containing the generated spatial effect variable is saved
in the current working directory under the defined name. In the default option, if the weighting matrix
is row-standardized, then the saved file is called SE_file_undirdyad_rowst.
If the weighting matrix is not row-standardized, then the saved file is called SE_file_undirdyad_norowst. 
Any previously existing file with the same name will be replaced.


{title:References}

{pstd}
Neumayer, Eric and Plümper, Thomas. 2010. Spatial Effects in Dyadic Data. {it}International Organization{sf} 64 (1), pp. 145-165.

{pstd}
Plümper, Thomas and Eric Neumayer. 2010. Model Specification in the Analysis of Spatial Dependence. {it}European Journal of Political Research{sf} 49 (3), pp. 418-442.

{title:Examples}

{phang}{cmd:. spundir y, w(exports) i(country_i) j(country_j) time(year) link(ik) sename(se_undirdyad) filename(se_undirdyad_file)}

{phang}{cmd:. spundir y, w(exports) i(country_i) j(country_j) time(year) link(mj) symmdyads norowst}

{phang}{cmd:. spundir y, w(exports) i(country_i) j(country_j) time(year) link(ik*jm) norowst nomerge}


{title:Authors}

{pstd}
Eric Neumayer{p_end}
{pstd}
Department of Geography and Environment{p_end}
{pstd}
London School of Economics and Political Science (LSE){p_end}
{pstd}
London WC2A 2AE, UK{p_end}
{pstd}
e.neumayer@lse.ac.uk{p_end}
{pstd}
{browse "http://personal.lse.ac.uk/neumayer"}{p_end}

{pstd}
Thomas Plümper{p_end}
{pstd}
Department of Government{p_end}
{pstd}
University of Essex{p_end}
{pstd}
Wivenhoe Park{p_end}
{pstd}
Colchester CO4 3SQ, UK{p_end}
{pstd}
tpluem@essex.ac.uk{p_end}
{pstd}
{browse "http://www.polsci.org/pluemper/"}{p_end}