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From | Richard Hiscock <richardjhiscock@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | st: capturing scalars in simulation |
Date | Sat, 23 Feb 2013 19:48:10 +1100 |
Hi all, I have method comparison data with haemoglobin level measured by three methods (pathology (1 reading), meth1 (3 readings) & meth2 (3 readings)) at the same time on the same subjects. Replicates are considered exchangeable within subject/method. As part of the analysis I am trying to create a dataset with a single reading for meth1 & meth2 which have been randomly sampled from within replicates for the subject & method. Then using concord[SJ 10-4 by T Steichen & N Cox] to obtain scalars for the mean difference & its SD + upper & lower limits of agreement I then wish to simulate this so as to obtain percentile based CI for these scalars (say 1000 reps) I have written the following program which successfully creates the datasets and when using noisily the analysis of each dataset occurs but I am unable to capture the scalars produced by concord except for one (the mean difference [listed as r(diff)] in concord program help file). Any guidance would be appreciated. thanks Richard Hiscock **TRY RANDOM selection from replicates capture program drop mysim1 *! mysim1 Bland-Altman LOA from random pairs RJH 23021013 program define mysim1, rclass version 12.1 drop _all use "file location", ** data in long format with id meth replicate *obtain random replicate for each of methods 2 & 3 (meth 1 single value) sort id meth by id meth : sample 1,count ** obtain requred estimates using concord program quietly reshape wide hb repl, i(id) j(meth) rename hb1 meth1 rename hb2 meth2 rename hb3 meth3 keep id meth* concord meth2 meth1, return scalar ll =r(LOA_ll) return scalar ul =r(LOA_ul) return scalar diff =r(diff) return scalar sd =r(sd_diff) return scalar n =r(N) end simulate ll =r(LOA_ll) ul =r(LOA_ul) diff =r(diff) sd =r(sd_diff) n =r(N) , reps(10) noisily : mysim1 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/