plm (version 1.6-5)

phtest: Hausman Test for Panel Models

Description

Specification test for panel models.

Usage

phtest(x, ...)
"phtest"(x, x2, ...)
"phtest"(x, data, model = c("within", "random"), method = c("chisq", "aux"), index = NULL, vcov = NULL, ...)

Arguments

x

an object of class "panelmodel" or "formula",

x2

an object of class "panelmodel",

model

a character vector containing the names of two models (length(model) must be 2),

data

a data.frame,

method

one of "chisq" or "aux",

index

an optional vector of index variables,

vcov

an optional covariance function,

...

further arguments to be passed on. For the formula method, place argument effect here to compare e.g. twoway models (effect = "twoways") Note: Argument effect is not respected in the panelmodel method.

Value

An object of class "htest".

Details

The Hausman test (sometimes also called Durbin--Wu--Hausman test) is based on the difference of the vectors of coefficients of two different models. The panelmodel method computes the original version of the test based on a quadratic form (Hausman (1978)). The formula method, if method="chisq" (default), computes the original version of the test based on a quadratic form; if method="aux" then the auxiliary-regression-based version in Wooldridge (2010, Sec. 10.7.3.) is computed instead. Only the latter can be robustified by specifying a robust covariance estimator as a function through the argument vcov (see Examples).

The equivalent tests in the one-way case using a between model (either "within vs. between" or "random vs. between") (see Hausman/Taylor (1981) or Baltagi (2013), Sec. 4.3) can also be performed by phtest, but only for test = "chisq", not for the regression-based test. NB: These equivalent tests using the between model do not extend to the two-ways case. (There are, however, some other equivalent tests, see Kang (1985) or Baltagi (2013), Sec. 4.3.7), but those are unsupported by phtest.)

References

Hausman, J.A. (1978), Specification tests in econometrics, Econometrica, 46(6), pp. 1251--1271.

Hausman, J.A./Taylor, W.E. (1981), Panel data and unobservable individual effects, Econometrica, 49(6), pp. 1377--1398.

Kang, Suk (1985), A note on the equivalence of specification tests in the two-factor multivariate variance components model, Journal of Econometrics, 28(2), pp. 193--203.

Wooldridge, Jeffrey M. (2010), Econometric analysis of cross-section and panel data, 2nd ed., MIT Press, Sec. 10.7.3., pp. 328--334. Baltagi, Badi H. (2013), Econometric Analysis of Panel Data, 5th ed., John Wiley and Sons., Sec. 4.3.

Examples

data("Gasoline", package = "plm")
form <- lgaspcar ~ lincomep + lrpmg + lcarpcap
wi <- plm(form, data = Gasoline, model = "within")
re <- plm(form, data = Gasoline, model = "random")
phtest(wi, re)
phtest(form, data = Gasoline)
phtest(form, data = Gasoline, method = "aux")

# robust Hausman test (regression-based)
phtest(form, data = Gasoline, method = "aux", vcov = vcovHC)

# robust Hausman test with vcov supplied as a
# function and additional parameters
phtest(form, data = Gasoline, method = "aux",
  vcov = function(x) vcovHC(x, method="white2", type="HC3"))