getXZ

boolean expression, set to TRUE if the instrument names
are to be extracted. Otherwise, the covariate names are
extracted.

inst

boolean expression, set to TRUE if the terms in the
formula <code>fm</code> should be returned instead of the variable
names.

terms

boolean expression, set to FALSE by
default. Indicates that the formula being considered is
constructed from a list of components, and thus the term
'intercept' is permitted.

components

Auxiliary function that takes in a two-sided formula, and extracts
the variable names of either the covariates or instruments. The
function returns an error if the formula includes a variable called
'intercept'.

The marginal treatment effect was introduced by Heckman and
Vytlacil (2005) <doi:10.1111/j.1468-0262.2005.00594.x> to provide a
choice-theoretic interpretation to instrumental variables models that
maintain the monotonicity condition of Imbens and Angrist (1994)
<doi:10.2307/2951620>. This interpretation can be used to extrapolate from
the compliers to estimate treatment effects for other subpopulations. This
package provides a flexible set of methods for conducting this
extrapolation. It allows for parametric or nonparametric sieve estimation,
and allows the user to maintain shape restrictions such as monotonicity. The
package operates in the general framework developed by Mogstad, Santos and
Torgovitsky (2018) <doi:10.3982/ECTA15463>, and accommodates either point
identification or partial identification (bounds). In the partially
identified case, bounds are computed using either linear programming
or quadratically constrained quadratic programming. Support for
four solvers is provided. Gurobi and the Gurobi R API
can be obtained from <http://www.gurobi.com/index>. CPLEX can be obtained
from <https://www.ibm.com/analytics/cplex-optimizer>. CPLEX R APIs 'Rcplex'
and 'cplexAPI' are available from CRAN. MOSEK and the MOSEK R API can be
obtained from <https://www.mosek.com/>. The lp_solve library is freely
available from <http://lpsolve.sourceforge.net/5.5/>, and is included when
installing its API 'lpSolveAPI', which is available from CRAN.

getXZ: Auxiliary function: extract X and Z covariates from a formula

Description

Usage

Arguments

Value