Get cheap starting values for a Wordfish model
initialize.urfish(tY)
| tY | a document by word matrix of counts |
|---|
List with elements:
starting values of alpha parameters
starting values of psi parameters
starting values of beta parameters
starting values for document positions
This function is only called by model fitting routines and does therefore not take a wfm classes. tY is assumed to be in document by term form.
In the poisson form of the model incidental parameters (alpha) are set to log(rowmeans/rowmeans[1]). intercept (psi) values are set to log(colmeans) These are subtracted from a the data matrix, which is logged and decomposed by SVD. Word slope (beta) and document position (theta) are estimated by rescaling SVD output.
This is substantially the method used by Slapin and Proksch's original code.
Will Lowe