Class "semi-continuous" and Inherited Classes
semi-continuous class inherits from the
continuous-class and is the parent of the
class, which in turn is the parent of the
SC_proportion class for semi-continuous variables. A semi-continuous variable has support on one or more point
masses and a continuous interval. The
semi-continuous class differs from the
truncated-continuous-class in that observations that fall on the point masses are bonafide data, rather than
indicators of censoring or truncation. If there are no observations that fall on a point mass, then either the
continuous-class or one of its other subclasses should be used. Aside from these facts, the rest of the
documentation here is primarily directed toward developers.
Objects from the Classes
Objects can be created that are of
SC_proportion class via the
missing_variable generic function by specifying
type = "semi-continuous"
type = "nonnegative-continuous",
type = "SC_proportion".
The semi-continuous class inherits from the continuous class and is intended for variables that, for example have a point mass at certain points and are continuous in between. Thus, its default transformation is the identity transformation, which is to say no transformation in practice. It has one additional slot.
Object of class
"ordered-categorical"that indicates whether an observed value falls on a point mass or the continuous interval in between. By convention, zero signifies an observation that falls within the continuous interval
At the moment, there are no methods for the semi-continuous class. However, the basic approach to modeling a semi-continuous variable has two steps. First, the indicator is modeled using the methods that are defined for it and its missing values are imputed. Second, the continuous part of the semi-continuous variable is modeled using the same techniques that are used when modeling continuous variables. Note that in the second step, only a subset of the observations are modeled, although this subset possibly includes values that were originally missing in which case they are imputed.
The nonnegative-continuous class inherits from the semi-continuous class, which has its point mass at zero and
is continuous over the positive real line. By default, the transformation for the positive part of a
nonnegative-continuuos variable is
log(y + a), where
a is a small constant determined by the
observed data. If a variable is strictly positive, the
positive-continuous-class should be used instead.
The SC_proportion class inherits from the nonnegative-continuous class. It has no additional slots, and the only supported
transformation function is the
(y * (n - 1) + .5) / n function. Its default
fit_model method is a
wrapper for the
betareg function in the betareg package. Its family must be
binomial so that its
link function can be passed to
If the observed values fall strictly on the open unit interval, the
proportion-class should be used instead.
Ben Goodrich and Jonathan Kropko, for this version, based on earlier versions written by Yu-Sung Su, Masanao Yajima, Maria Grazia Pittau, Jennifer Hill, and Andrew Gelman.
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