Abstract
We develop a test for a restricted functional form of a mean regression when a complex distributional model for all variables is estimated. The test statistic is an average squared deviation from the estimated hypothesized function of the form implied by the estimated parametric model, and is asymptotically distributed as a mixture of χ2 distributions. The test is easy to implement using numerical derivatives, and it performs well in samples of typical size. We illustrate the test using data on labor market characteristics of US young men.
Acknowledgement
I am grateful to the Co-Editor and two anonymous referees for useful suggestions that significantly improved the presentation. I also thank Nikolay Kudrin for excellent research assistance.
A Appendix
Proofs
Proof of Lemma 1
Consistency and asymptotic normality of
Proof of Lemma 2
Note that
which follows from Assumption 3. Next,
which follows from the previous and Assumption 2(f). Finally,
Now,
by Assumption 2(d) and Assumption 3. Then, by Lemma 4.3 of Newey and McFadden (1994),
Proof of Theorem 1
Take a second-order stochastic expansion of n
where
and
Finally,
by the law of large numbers (see the proof of Lemma 2) and because
Summarizing, we have that under H0,
Now, using Lemma 3.2 from Vuong (1989), we get that
where
Proof of Theorem 2
It follows from the proof of Theorem 1 that
Because
B Appendix
Details on Simulation Experiments
Consider the setup of the first experiment. Because
Note that there are only two non-collinear elements. Hence,
which, expectedly, has a rank of 2.
The logdensity is
and its derivatives are
Then
The derivatives of the hypothesized regression function are
and hence
So, the (minus) inverted Hessian is
Next we compute
Hence, the matrix of expected cross-products of the elements of the score vector is
Then the asymptotic variance matrix is
and, consequently,
For the second experiment, we extend the method of Anatolyev and Gospodinov (2010) of constructing a joint distribution of mixed discrete and continuous marginals to the cases of the cardinality of the discrete marginal’s support higher than two. The joint CDF/CMF is
so the PDF/PMF is a derivative with respect to the continuous argument and a difference with respect to the discrete one:
where the second term is
or
For the FGM copula,
implying the distorted success probabilities
The joint density/mass is
and the result follows.
C Appendix
Details on Empirical Illustration
We omit the parameters during the derivations. In the case of only one discrete component, the joint PDF/PMF is
where the last term is
The Gaussian copula is
This leads to
Then,
Note that because Φ2 is bivariate standard normal with correlation coefficient ϱ, we have, by normality of the conditional distributions under joint normality, that
and hence
In the case of two discrete components, the joint PDF/PMF is
where the last term is
Consider the three-dimensional Gaussian copula
Note the property
which leads to
Then,
As a computational matter, we use the fact that
where
and that
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