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10-22-2012 11:26 PM

I couldn't understand the following content of statistical method with yellow background in the paper:

We evaluated the continuous association between eGFR using both equations and incidence rates of clinical outcomes using a Poisson regression model incorporating linear spline terms for eGFR (knots at 45, 60, 75, 90, and 105 mL/min/1.73 m2) with and without adjustment for age, sex,and race.

note:eGFR (estimated Glomerular Filtration Rate) could be calculated using different equations based on serum creatinine, age, sex, race.

please explain the statistical method and thanks a lot.

In addition, I have another question about how to get adjusted incidence rate ratios for all-cause mortality after adjusting for some covariates like age, sex, diabetes, etc. As far as I am concerned, I could perform Logistic/Cox regression for death or other outcome (Y: die-0, and survive-1; X: covariates). But I have no idea about incidence rate ratio for all-cause mortality using regression.

please give some advice about it. Thank you so much.

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10-23-2012 10:46 AM

You can do a Poisson regression using GENMOD. In the simplest terms, it means using a Poisson distribution for the error terms rather than the normal one. More details are in the GENMOD references.

Here is an introduction to splines

http://www.sas.com/offices/NA/canada/downloads/presentations/TDM2009/Spline_Modeling.pdf

You can find more by just searching support.sas.com for linear splines.

I need more context for your second question; it is too unclear to comment on. Ratio between 'what' rates? Logistic regression would give you an estimate of one rate.

Doc Muhlbaier

Duke

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10-23-2012 10:32 PM

Hi, Doc

Thank you so much for your answer to the first question. It is very useful and important for me to learn spline further.

For the second question, I attach a figure of table from the paper that described the multivariate analysis of Incidence Rate for Outcomes like end-stage renal disease, all-cause mortality, stroke, etc. In this context, eGFR (estimated Glomerular Filtration Rate) could be calculated using different equations (MDRD equation and CKD-EPI equation) based on serum creatinine, age, sex, race. So, there were two different eGFR values for one patient. eGFR was divided into 5 groups (>=120, 119-90, 89-60, 59-30, <30) and the group of 119-89 was defined as reference group in the multivariate analysis. I was confused with how to adjust incidence rate of outcome like all-cause death or Stroke. Just as you said, Logistic regression would give me an estimate of one rate. what is y in equation of logisitic regression for estimate of one rate? I know that y is usually variate (Yes or No, 1 or 0, death or survival) . please give some advice about it.please give some advice about it. If the information of figure is not enough, I attached the fulltext of the paper

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10-24-2012 09:21 AM

If a case/each observation/ a subject was related to differert time like different follow-up time, We would choose poission regression rather than logistic regression. Is it right?

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10-25-2012 09:44 AM

They used Poisson regression to compute the risk adjusted incidence rate of each outcome. The ratio part is in comparing the adjusted rate for a category to the reference rate.

If you want more on the methods used, you should to contact the authors directly; as they didn't even use SAS for the analysis.