The function tobit
is a convenience interface to survreg
(for survival regression, including censored regression) setting different
defaults and providing a more convenient interface for specification
of the censoring information.
The default is the classical tobit model (Tobin 1958, Greene 2003) assuming
a normal distribution for the dependent variable with left-censoring at 0.
Technically, the formula of type y ~ x1 + x2 + …
passed to tobit
is simply transformed into a formula suitable for survreg
: This means
the dependent variable is first censored and then wrapped into a Surv
object containing the censoring information which is subsequently passed to
survreg
, e.g., Surv(ifelse(y <= 0, 0, y), y > 0, type = "left") ~ x1 + x2 + …
for the default settings.