textmodel_wordfish: Wordfish text model

In quanteda.textmodels: Scaling Models and Classifiers for Textual Data

Wordfish text model

Description

Estimate Slapin and Proksch's (2008) "wordfish" Poisson scaling model of one-dimensional document positions using conditional maximum likelihood.

Usage

textmodel_wordfish(
  x,
  dir = c(1, 2),
  priors = c(Inf, Inf, 3, 1),
  tol = c(1e-06, 1e-08),
  dispersion = c("poisson", "quasipoisson"),
  dispersion_level = c("feature", "overall"),
  dispersion_floor = 0,
  abs_err = FALSE,
  residual_floor = 0.5
)

Arguments

x	the dfm on which the model will be fit
dir	set global identification by specifying the indexes for a pair of documents such that \hat{\theta}_{dir[1]} < \hat{\theta}_{dir[2]}.
priors	prior precisions for the estimated parameters \alpha_i, \psi_j, \beta_j, and \theta_i, where i indexes documents and j indexes features
tol	tolerances for convergence. The first value is a convergence threshold for the log-posterior of the model, the second value is the tolerance in the difference in parameter values from the iterative conditional maximum likelihood (from conditionally estimating document-level, then feature-level parameters).
dispersion	sets whether a quasi-Poisson quasi-likelihood should be used based on a single dispersion parameter ("poisson"), or quasi-Poisson ("quasipoisson")
dispersion_level	sets the unit level for the dispersion parameter, options are "feature" for term-level variances, or "overall" for a single dispersion parameter
dispersion_floor	constraint for the minimal underdispersion multiplier in the quasi-Poisson model. Used to minimize the distorting effect of terms with rare term or document frequencies that appear to be severely underdispersed. Default is 0, but this only applies if dispersion = "quasipoisson".
abs_err	specifies how the convergence is considered
residual_floor	specifies the threshold for residual matrix when calculating the svds, only applies when sparse = TRUE

Details

The returns match those of Will Lowe's R implementation of wordfish (see the austin package), except that here we have renamed words to be features. (This return list may change.) We have also followed the practice begun with Slapin and Proksch's early implementation of the model that used a regularization parameter of se(\sigma) = 3, through the third element in priors.

Value

An object of class textmodel_fitted_wordfish. This is a list containing:

dir	global identification of the dimension
theta	estimated document positions
alpha	estimated document fixed effects
beta	estimated feature marginal effects
psi	estimated word fixed effects
docs	document labels
features	feature labels
sigma	regularization parameter for betas in Poisson form
ll	log likelihood at convergence
se.theta	standard errors for theta-hats
x	dfm to which the model was fit

Note

In the rare situation where a warning message of "The algorithm did not converge." shows up, removing some documents may work.

Author(s)

Benjamin Lauderdale, Haiyan Wang, and Kenneth Benoit

References

Slapin, J. & Proksch, S.O. (2008). A Scaling Model for Estimating Time-Series Party Positions from Texts. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1111/j.1540-5907.2008.00338.x")}. American Journal of Political Science, 52(3), 705–772.

Lowe, W. & Benoit, K.R. (2013). Validating Estimates of Latent Traits from Textual Data Using Human Judgment as a Benchmark. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1093/pan/mpt002")}. Political Analysis, 21(3), 298–313.

See Also

predict.textmodel_wordfish()

Examples

(tmod1 <- textmodel_wordfish(quanteda::data_dfm_lbgexample, dir = c(1,5)))
summary(tmod1, n = 10)
coef(tmod1)
predict(tmod1)
predict(tmod1, se.fit = TRUE)
predict(tmod1, interval = "confidence")

## Not run: 
library("quanteda")
dfmat <- dfm(tokens(data_corpus_irishbudget2010))
(tmod2 <- textmodel_wordfish(dfmat, dir = c(6,5)))
(tmod3 <- textmodel_wordfish(dfmat, dir = c(6,5),
                             dispersion = "quasipoisson", dispersion_floor = 0))
(tmod4 <- textmodel_wordfish(dfmat, dir = c(6,5),
                             dispersion = "quasipoisson", dispersion_floor = .5))
plot(tmod3$phi, tmod4$phi, xlab = "Min underdispersion = 0", ylab = "Min underdispersion = .5",
     xlim = c(0, 1.0), ylim = c(0, 1.0))
plot(tmod3$phi, tmod4$phi, xlab = "Min underdispersion = 0", ylab = "Min underdispersion = .5",
     xlim = c(0, 1.0), ylim = c(0, 1.0), type = "n")
underdispersedTerms <- sample(which(tmod3$phi < 1.0), 5)
which(featnames(dfmat) %in% names(topfeatures(dfmat, 20)))
text(tmod3$phi, tmod4$phi, tmod3$features,
     cex = .8, xlim = c(0, 1.0), ylim = c(0, 1.0), col = "grey90")
text(tmod3$phi['underdispersedTerms'], tmod4$phi['underdispersedTerms'],
     tmod3$features['underdispersedTerms'],
     cex = .8, xlim = c(0, 1.0), ylim = c(0, 1.0), col = "black")
if (requireNamespace("austin")) {
    tmod5 <- austin::wordfish(quanteda::as.wfm(dfmat), dir = c(6, 5))
    cor(tmod1$theta, tmod5$theta)
}
## End(Not run)

quanteda.textmodels documentation built on Sept. 11, 2024, 8:19 p.m.