Date:         Sun, 29 Oct 2006 10:17:57 -0500
Reply-To:     Marina Kekrou <mkekrou@YAHOO.CO.UK>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Marina Kekrou <mkekrou@YAHOO.CO.UK>
Subject:      Re: SPEC to test for heteroscedasticity
Comments: To: "David L. Cassell" <davidlcassell@MSN.COM>

Hi,

Thanks for your reply.

I include year and industry dummies in my model. When I drop the dummies,
there is no problem at all when using the spec test. However, I want to
include year and industries effects. So I checked my data by year and
industry and dropped years/industries with relatively few observations to
see if this is causing the problem but the average covariane matrix is
still singular.

Any ideas?

Thanks.