Deat Jun,the covariance?

Dear Jun: Sorry for making you in the reading trouble: Here is my question: Is there any special specification on the employ of covariance: The papers which I have read most always take the covariance excluded,such as W21,w31 w32.If the Decrease of OFV between the model of the covriance included and the one not is significantly meaningful,what choice should I do? I really do not understand the correlation of Cl and V,if the convariance between the two parameters does exist.Dose it truly exist in physiologically or just mathematically? Dear Hongpo, I am not sure I understand your question. Can you rephrase? Jun Shen Millipore Corporation 2009/12/13 yhb5442387 <[email protected]> Dear professor: THE off diagnoal: Sometimes we make the OMEGA syntax as follows:$omega 0.1 0.1,but $omega blokc (2) 0.1 0.01 0.1 at another occasion.As we know,the only difference is whether the off diagonal estimate be used.So is there any specila condition about the existence of the W21,or some another W square like that? Thank you !!! -- 工作和生活,都要开心的过. 你好,叶红波在此送上真挚的祝福.祝你开心, 叶红波