lmmot (version 0.1.4)

lmmot: Multiple Ordinal Tobit Model

Description

Fit right censored Multiple Ordinal Tobit (MOT) model.

Usage

lmmot(formula, data = sys.frame(sys.parent()), threshold, stdEr = "fisher",
  ...)

Arguments

formula

Object of class formula describing the model.

data

Optional data frame or environment containing the variables in the model.

threshold

Vector of thresholds in the model.

stdEr

Method for standard error estimation. Use "fisher" for estimation using the inverse of the Fisher information matrix or "hessian" for estimation using the Hessian matrix.

...

Further arguments passed to the maximum likelihood estimation function maxLik.

Value

lmmot object: maxLik object with additional fields:

• censoring: Number of obeservations in the censoring intervals.
• fisherInfo: Fisher information matrix.
• stdEr: Standard errors for estimated coefficients.
• tval: Value for t statistic in Wald test.
• pval: p-value in Wald test.
• fitted.values: Fitted values of the estimated model.
• residuals: Residuals of the estimated model.

Details

Fit right censored Multiple Ordinal Tobit (MOT) model. The model is a right censored Tobit model with multiple ordinal categories for latent values above the threshold, the threshold is therefore replaced by a threshold vector.

For the latent variable a linear model with independent and identically distributed non-systematic and homoscedastic errors is assumed.

If the threshold is of length 1, the model is equivalent to the standard right censored Tobit model.

The data is fitted with the Maximum Likelihood method.

See Also

lm maxLik

Examples

# Random data for x
N <- 100
x <- rnorm(N, 25, 10)

# Simulate data for latent variable ystar with simple linear model
beta_0 <- 60
beta_1 <- 1
sigma <- 8
ystar <- beta_0 + beta_1*x + rnorm(N, 0, sigma)

# Simulate censoring for observed variable y
y <- ystar
y[y >= 100] <- 100
y[(y >= 90) & (y < 100)] <- 90
y[(y >= 80) & (y < 90)] <- 80

# MOT regression with observed variable y
mot.fit <- lmmot(y ~ x, threshold = c(80, 90, 100))

# Show details
summary(mot.fit)

# Compare real data with model fit 
plot(x, ystar)
abline(coefficients(mot.fit)[1:2])