Title
frm_ptest -- P test for non-nested one-part and two-part fractional regression models
Syntax
frm_ptest, mod1(name_model1a [name_model1b]) mod2(name_model2a [name_model2b]) [options]
options Description ------------------------------------------------------------------------- lm specify the LM version of the P test to be performed wald specify the t version of the P test to be performed -------------------------------------------------------------------------
where name_mod1a, name_mod1b, name_mod2a and name_mod2b are names under which estimation results were saved via estimates store. The second name in mod1 and mod2 is only to be provided when testing the full specification of two-part models.
Description
frm_ptest applies the P test statistic proposed by Davidson and MacKinnon (1981) to fractional regression models estimated via frm. frm_ptest may be used to test against each other two alternative specifications for the link function in: (i) one-part fractional regression models; (ii) the binary component of two-part fractional regression models; (iii) the fractional component of two-part fractional regression models; and (iv) two-part fractional regression models. In addition, frm_ptest may be used to test one-part models against two-part models. See Ramalho, Ramalho and Murteira (2011) for details on the application of the P test in the fractional regression framework.
Options
lm specifies that the LM version of the P test is to be performed. Unless the competing models are alternative specifications for the binary component of a two-part fractional regression model, a robust LM test is implemented.
wald specifies that the robust t version of the P test is to be performed. This is the default option.
Examples
Setup - data used in Ramalho, Ramalho and Henriques (2010) . use http://evunix.uevora.pt/~jsr/stata/JPA-2010.dta
Testing logit versus loglog specifications for standard fractional regression models . frm SCORE LANDLORD LIVESTOCK CROP SIZE SUBSIDIES ALTO CENTRAL BAIXO . estimates store a1 . frm SCORE LANDLORD LIVESTOCK CROP SIZE SUBSIDIES ALTO CENTRAL BAIXO, linkf(loglog) . estimates store a2 . frm_ptest, mod1(a1) mod2(a2)
Testing a logit one-part fractional regression model versus a binary logit + fractional probit two-part model . frm SCORE LANDLORD LIVESTOCK CROP SIZE SUBSIDIES ALTO CENTRAL BAIXO . estimates store a1 . frm SCORE LANDLORD LIVESTOCK CROP SIZE SUBSIDIES ALTO CENTRAL BAIXO, m(2Pbin) inf(1) . estimates store a2 . frm SCORE LANDLORD LIVESTOCK CROP SIZE SUBSIDIES ALTO CENTRAL BAIXO, m(2Pfrac) linkf(probit) inf(1) . estimates store a3 . frm_ptest, mod1(a1) mod2(a2 a3)
Saved results
frm_ptest saves the following in r() if both LM and Wald versions of the P test are performed:
Scalars r(t1) t statistic for testing mod1 against model mod2 r(t1p) p-value for the statistic r(t1) r(t2) t statistic for testing mod2 against model mod1 r(t2p) p-value for the statistic r(t2) r(LM1) LM statistic for testing mod1 against model mod2 r(LM1p) p-value for the statistic r(LM1) r(LM2) LM statistic for testing mod2 against model mod1 r(LM2p) p-value for the statistic r(LM2)
Author
Joaquim J.S. Ramalho Department of Economics University of Evora Portugal jsr@uevora.pt
Remarks
frm_ptest is not an official Stata command. For further help and support, please contact the author. Please notice that this software is provided as is, without warranty of any kind, expressed or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose, and noninfringement. In no event shall the author be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the software or the use or other dealings in the software.
References
Davidson, R. and J.G. MacKinnon (1981), "Several tests for model specification on the presence of alternative hypotheses", Econometrica, 49(3), 781-793.
Ramalho, E.A., J.J.S. Ramalho and J.M.R. Murteira (2011), "Alternative estimating and testing empirical strategies for fractional regression models", Journal of Economic Surveys, 25(1), 19-68.
Ramalho, E.A., J.J.S. Ramalho and P.D. Henriques (2010), "Fractional regression models for second stage DEA efficiency analyses", Journal of Productivity Analysis, 34(3), 239-255.
Also see