目前日期文章:200601 (2)

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I construct a new category to put some articles of my statistical
consulting experiences.



It's not only a memory, but also a record that I can retrospect
some special cases or problems if I encounter some similar
situations in the future.



I'll write these articles in my office and type in English. It
doesn't mean I am show off my English ability because there is no
Chinese input software in the computer in my office.



Don't feel picky in my grammar and spelling. I recognize my English
is poor. Well, if there is any suggestion from someone, welcome to
leave your message in relative articles.












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Marianne, a postdoc in the School of Nursing in UNC-CH. She lives in Virginia now. Her study is a comparison of urban and rural hospitals' nurse work environment and quality of care. I consult this case from last December.




The model she fits is a hierarchical regression model with generalized estimating equation (GEE). GEE method is very popular in model fitting when independent variables are highly correlated and there are many missing data in data set as well. It was created by Kung-Yi Liang, a Taiwanese who is a professor in the department of biostatistics in Johns Hopkins University.




Today, Marianne sent an email and show an error message in her SAS output. The problem is that the Hessian matrix is semi positive definite, and the program is terminated. I once encountered this situation before, but I don't know how to solve it so far. My supervisor, Mark, told me it is appeared when there are some empty cells in some categorical independent variables vs. categorical dependent variable. We can use PROC FREQ in SAS to check what IV has empty cells, then delete it.




As what Mark said, there is an empty cell in an IV. After deleting it, the output is shown without any error message.




It's a great experiment of fitting model. Thanks Mark!












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