 1
1
 is a linear function for
 is a linear function for
 ,
where
,
where  is any matrix, and
 is any matrix, and  is a matrix such that
 is a matrix such that 
 .
This condition holds, for example, if the marginal distribution of
.
This condition holds, for example, if the marginal distribution of  is
normal, although that assumption is much stronger than is needed.  See Cook
(1998), Cook and Weisberg (1994, 1999) for more discussion.
 is
normal, although that assumption is much stronger than is needed.  See Cook
(1998), Cook and Weisberg (1994, 1999) for more discussion.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .