#' Interface between ls model and Zelig
#' This function is exclusively for use by the `zelig' function
#' @param formula a formula
#' @param weights a numeric vector
#' @param ... ignored parameters
#' @param data a data.frame
#' @return a list to be coerced into a zelig.call object
#' @export
#' @author Matt Owen \email{mowen@@iq.harvard.edu}
zelig2ls <- function(formula, ..., data, weights=NULL)
z(
lm,
formula = formula,
weights = weights,
model = F,
data = data
)
#' Param Method for the 'ls' Zelig Model
#' @note This method currently returns via a deprectated style
#' @usage \method{param}{ls}(obj, num, \dots)
#' @S3method param ls
#' @param obj a 'zelig' object
#' @param num an integer specifying the number of simulations to sample
#' @param ... ignored parameters
#' @return a list to be cast as a 'parameters' object
#' @author Matt Owen \email{mowen@@iq.harvard.edu}
param.ls <- function(obj, num, ...) {
mvrnorm(n=num, mu=coef(.object), Sigma=vcov(.object))
}
#' Compute quantities of interest for 'ls' Zelig models
#' @usage \method{qi}{ls}(obj, x, x1=NULL, y=NULL, num=1000, param=NULL)
#' @S3method qi ls
#' @param obj a \code{zelig} object
#' @param x a 'setx' object or NULL
#' @param x1 an optional 'setx' object
#' @param y this parameter is reserved for simulating average treatment effects,
#' though this feature is currentlysupported by only a handful of models
#' @param num an integer specifying the number of simulations to compute
#' @param param a parameters object
#' @return a list of key-value pairs specifying pairing titles of quantities of
#' interest with their simulations
#' @author Matt Owen \email{mowen@@iq.harvard.edu}
qi.ls <- function(obj, x, x1=NULL, y=NULL, num=1000, param=NULL) {
# error-catching
if (missing(x))
stop("x cannot be missing while computing the `ls' model")
# Get coefficients of the linear model
coefs <- coef(param)
# compute expected value
ev <- coefs %*% t(x)
ev1 <- NA
fd <- NA
if (!is.null(x1)) {
ev1 <- coefs %*% t(x1)
fd <- ev1 - ev
}
# return
list("Expected Values: E(Y|X)" = ev,
"Expected Values: E(Y|X1)" = ev1,
"Predicted Values: Y|X" = ev,
"Predicted Values: Y|X1" = ev1,
"First Differences: E(Y|X1) - E(Y|X)" = fd
)
}
#' Describe a \code{ls} model to Zelig
#' @note \code{ls} stands for "least squares fit"
#' @usage \method{describe}{ls}(...)
#' @S3method describe ls
#' @param ... ignored parameters
#' @return a list to be processed by \code{as.description}
#' @author Matt Owen \email{mowen@@iq.harvard.edu}
#' @export
describe.ls <- function(...){
parameters <-list(mu = list(
equations = c(1,1),
tags.allowed = FALSE,
dep.vars = TRUE,
exp.vars = TRUE
)
)
# return
list(authors = c("Kosuke Imai", "Gary King", "Olivia Lau"),
year = 2007,
category = "continuous",
parameters = parameters,
text = "Least Squares Regression for Continuous Dependent Variables"
)
}
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