Keywords - Function groups - @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Library: metrics
See also: heckman select andrews sssm gennorm dwade

Quantlet: powell
Description: powell calculates the semiparametric estimator proposed by Powell (1987) of the slope coefficients of the outcome equation in a sample selection model.

Usage: b = powell(x,y,id,h)
Input:
x n x M regressor matrix. WARNING: x may not contain a vector of ones!
id n x 1 vector containing the estimated index of the first-step selection equation.
y n x 1 matrix containing n observ. of the dependent variable
h scalar, the bandwidth
Output:
b M x 1 vector of estimated slope coefficients

Example:



library("xplore")

library("metrics")

randomize(66666)

n	= 200				; sample size

ss1	= #(1,0.9)~#(0.9,1)		; covariance matrix of error terms

g	= #(1)				; true coefficient of decision equation

b	= #(-9, 1)			; true intercept and slope of outcome equation

u	= gennorm(n, #(0,0), ss1)	; generate realizations of joint distribution of error terms

ss2     = #(1,0.4)~#(0.4,1)		; covariance matrix of regressors

xz      = gennorm(n, #(0,0), ss2)       ; generate realizations of joint distribution of regressors

z       = xz[,2]			; regressor of decision equation

q       = (z*g+u[,1].>=0)		; generate binary dependent variable of decision equation

hd	= 0.1*(max(z) - min(z))		; bandwidth for dwade procedure

d	= dwade(z,q,hd)*(2*sqrt(3)*pi)	; dwade estimate * scaling factor

id	= z*d				; estimated first-step index

h       = 0.2*(max(id) - min(id))	;  bandwidth for powell procedure

x	= matrix(n)~xz[,1]		; regressors for outcome equation

y       = x*b+u[,2]			; dependent variable for outcome equation

zz	= paf(y~x~id, q)		; impose censored sampling

y	= zz[,1]

x	= zz[,3:(cols(zz)-1)]

id	= zz[,cols(zz)]		

b	= powell(x,y,id,h)

b					; estimated slope coefficient

Result:

estimated slope of the outcome equation of a semiparametric

sample selection model according to Ahn and Powel (1993)


Library: metrics
See also: heckman select andrews sssm gennorm dwade

Keywords - Function groups - @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Author: akw,961011
(C) MD*TECH Method and Data Technologies, 21.9.2000