topic Re: Unbiased medians for nhanes subgroups? in SAS Programming

Unbiased medians for nhanes subgroups?

ProfB — Thu, 24 Jul 2014 21:20:09 GMT

I'm trying to generate median values for urine trace elements using NHANES data. Proc surveymeans does not produce quantiles when a domain statement is used and employment of 'where' or 'class' disrupts the weights and does not produce population representative medians. So....I'm stuck. Any advice on how I can generate unbiased medians for age/gender subgroups? Thanks much.

Re: Unbiased medians for nhanes subgroups?

ballardw — Thu, 24 Jul 2014 22:42:07 GMT

I suspect the issue of the domain analysis and quantiles revolves around the confidencle limits and variability and such combined with the treatments of ties.

Since median is a central measure AND unless you need confidence limits I would start with Proc Means with the weights and your domain variable as a class variable. Generally the central measures don't vary between Means and SurveyMeans.

Re: Unbiased medians for nhanes subgroups?

ProfB — Thu, 24 Jul 2014 22:52:44 GMT

Thanks very much, How would you suggest I handle the clustering?

Re: Unbiased medians for nhanes subgroups?

ballardw — Fri, 25 Jul 2014 17:20:51 GMT

By clustering do you mean the Age group in your example? I would normally think of that as a domain variable as cluster with survey procs relates to sampling design. Does NHANES use a cluster sample design?

Any way, clustering is just factor in the calculations for variability, not the central measure. So even with a cluster design I don't think it will effect the actual median.