An Ancillarity Paradox Which Appears in Multiple Linear Regression
Brown, Lawrence D.
Ann. Statist., Tome 18 (1990) no. 1, p. 471-493 / Harvested from Project Euclid
Consider a multiple linear regression in which $Y_i, i = 1, \cdots, n$, are independent normal variables with variance $\sigma^2$ and $E(Y_i) = \alpha + V'_i\beta$, where $V_i \in \mathbb{R}^r$ and $\beta \in \mathbb{R}^r.$ Let $\hat{\alpha}$ denote the usual least squares estimator of $\alpha$. Suppose that $V_i$ are themselves observations of independent multivariate normal random variables with mean 0 and known, nonsingular covariance matrix $\theta$. Then $\hat{\alpha}$ is admissible under squared error loss if $r \geq 2$. Several estimators dominating $\hat{\alpha}$ when $r \geq 3$ are presented. Analogous results are presented for the case where $\sigma^2$ or $\theta$ are unknown and some other generalizations are also considered. It is noted that some of these results for $r \geq 3$ appear in earlier papers of Baranchik and of Takada. $\{V_i\}$ are ancillary statistics in the above setting. Hence admissibility of $\hat{\alpha}$ depends on the distribution of the ancillary statistics, since if $\{V_i\}$ is fixed instead of random, then $\hat{\alpha}$ is admissible. This fact contradicts a widely held notion about ancillary statistics; some interpretations and consequences of this paradox are briefly discussed.
Publié le : 1990-06-14
Classification:  Admissibility,  ancillary statistics,  multiple linear regression,  62C15,  62C20,  62F10,  62A99,  62H12,  62J05
@article{1176347602,
     author = {Brown, Lawrence D.},
     title = {An Ancillarity Paradox Which Appears in Multiple Linear Regression},
     journal = {Ann. Statist.},
     volume = {18},
     number = {1},
     year = {1990},
     pages = { 471-493},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1176347602}
}
Brown, Lawrence D. An Ancillarity Paradox Which Appears in Multiple Linear Regression. Ann. Statist., Tome 18 (1990) no. 1, pp.  471-493. http://gdmltest.u-ga.fr/item/1176347602/