Title
spdir - Creates directed dyad contagion spatial effect variable
Syntax
spdir lagvar [if] [in], weightvar(varname) source(varname) target(varname) link(options)
[options]
options Description ------------------------------------------------------------------------- time(varname) contains the numeric time variable exclusive exclusive directed dyad contagion norowst spatial effect variable not row-standardized nomerge no automatic merge of spatial effect variable into original dataset sename(name) name to be given to created spatial effect variable labelname(name) name of label given to spatial effect variable filename(name) name of file to which spatial effect variable saved -------------------------------------------------------------------------
Description
spdir generates a directed dyad contagion spatial effect variable for analysis of spatial dependence in directed 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 directed dyad data. See Plümper and Neumayer (2010) for a discussion of model specification in the analysis of spatial dependence. Users must have mmerge.ado already installed. If not, type net search mmerge.ado into the editor and install.
Additional information
See http://personal.lse.ac.uk/neumayer/spdir.htm.
Arguments
lagvar is the variable to be spatially lagged. It is the directed dyadic dependent variable in spatial lag models, a selected independent variable in spatial-x models and a saved regression residual in spatial error models.
weightvar(varname) is the weighting or connectivity variable linking source unit i with target unit j. It must be numeric and must not contain negative values. It may or may not be directed.
source(varname) is the identifying variable of source unit i. It can be a numeric or string variable.
target(varname) is the identifying variable of target unit j. It can be a numeric or string variable.
Options
link(options) is required. The following options are allowed: ik, ki, im, mi, jm, mj, jk, kj. Option ik requests that the virtually transformed weighting variable weightvar(varname) is to represent connectivity from source unit i to other source units k. Option ki requests connectivity from other source units k to source unit i. Option im requests connectivity from source unit i to target units m. Option mi requests connectivity from target units m to source unit i. Option jm requests connectivity from target unit j to other target units m. Option mj requests connectivity from other target units m to target unit j. Option jk requests connectivity from target unit j to source units k. Option kj requests connectivity from source units m to target unit j. Which of these options is appropriate depends on the specific hypothesis of spatial dependence to be tested. Researchers can request the sum or product of any two of these connectivities by listing the first one, then either + or * and then the second link. For example, option ik+jm requests that the weighting matrix represents the sum of connectivities invoked by ik and jm. Option ik*kj requests that the weighting matrix represents the product of connectivities invoked by ik and kj. The order does not matter, i.e., option ik+jm is the same as option jm+ik. The same links cannot be combined with each other, i.e., ik+ik is not an allowed option.
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.
exclusive specifies that all dyads containing either i or j as either source or target are excluded from having a spatial effect on dyad ij.
norowst 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.
nomerge requests that the generated spatial effect variable is not automatically merged into the original data set.
sename(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_dirdyad_rowst. If the weighting matrix is not row-standardized, then the spatial effect variable is called SE_var_dirdyad_norowst. Any previously existing variable with the same name will be replaced.
labelname(name) names the label of the generated spatial effect variable. The default label given is "Directed dyad contagion spatial effect variable".
filename(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 a file is saved in the current working directory called SE_file_dirdyad_rowst. If the weighting matrix is not row-standardized, then the saved file is called SE_file_dirdyad_norowst. Any previously existing file with the same name will be replaced.
References
Neumayer, Eric and Plümper, Thomas. 2010. Spatial Effects in Dyadic Data. International Organization 64 (1), pp. 145-165.
Plümper, Thomas and Eric Neumayer. 2010. Model Specification in the Analysis of Spatial Dependence. European Journal of Political Research 49 (3), pp. 418-442.
Examples
. spdir y, w(exports) s(source_country) t(target_country) link(ik) sename(se_dirdyad) filename(dirdyad_file)
. spdir y, w(exports) s(source_country) t(target_country) time(year) link(jm) norowst
. spdir y, w(exports) s(source_country) t(target_country) time(year) link(ik*jm) nomerge
Authors
Eric Neumayer Department of Geography and Environment London School of Economics and Political Science (LSE) London WC2A 2AE, UK e.neumayer@lse.ac.uk http://personal.lse.ac.uk/neumayer
Thomas Plümper Department of Government University of Essex Wivenhoe Park Colchester CO4 3SQ, UK tpluem@essex.ac.uk http://www.polsci.org/pluemper/