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From | Phil Clayton <philclayton@internode.on.net> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Controling precision for multiple runs of same code |
Date | Tue, 4 Jun 2013 10:05:28 +1000 |
The first thing that stands out is: merge m:m ... You should pretty much never do this. Don't take my word for it - the manual entry for -merge- says "m:m specifies a many-to-many merge and is a bad idea" and explains why, including that you might get non-reproducible results. You probably want m:1. If for some reason you definitely need to join all records in a many-to-many fashion based on one or more ID variables, you should use -joinby-. Phil On 04/06/2013, at 9:55 AM, Melanie Leis <melanieleis@gmail.com> wrote: > Hello, > > I'm having trouble with a section of my code that yields different > results each time I run it. > > I start out with a dataset, baseline_4.dta, which has 47,267,047 > observations and 16 variables, and run this: > > merge m:m statefips agecat_census using "ABCD.dta" > assert _merge==3 > drop _merge > egen tot_pop=sum(pop), by(statefips countyfips agecat_census sexcat > racecat iprcat_mpact iprcat coverage groupsize) > checkpop > rename pop oldpop > gen pop=tot_pop*prob_agecat_mpact > checkpop > collapse (sum) pop, by(statefips countyfips agecat_mpact sexcat > racecat iprcat_mpact iprcat coverage groupsize) > checkpop > sum > sort _all > save "baseline_5.dta", replace > > checkpop is a program that tells me what my total population is each > time I run it. My total population is the same before and after the > collapse function (see results below). > > At the end, my total population and my number of observations in > baseline_5.dta is different every time I run this. I suspect the > difference is in rounding when it executes the gen pop line, but I've > tried replacing it for > > gen double pop=tot_pop*prob_agecat_mpact > > and > > gen float pop=tot_pop*prob_agecat_mpact > > And I still get differences. > > I tried using > > gen long pop=tot_pop*prob_acegat_mpact > > But I lost too much precision by doing this. > > Could you please recommend a solution to obtain the exact same numbers > in each run, without sacrificing precision? > > Thanks! > > Melanie > > The log file for 2 of the runs I've done: > > ************* RUN A *********************** > > . merge m:m statefips agecat_census using "ABCD.dta" > > Result # of obs. > ----------------------------------------- > not matched 0 > matched 47,267,047 (_merge==3) > ----------------------------------------- > > . assert _merge==3 > > . drop _merge > > . egen tot_pop=sum(pop), by(statefips countyfips agecat_census sexcat > racecat iprcat_mpac >> t iprcat coverage groupsize) > > . checkpop > > Total pop: 347,095,179 > Observations: 47,267,047 > Missing: 0 > > . rename pop oldpop > > . gen pop=tot_pop*prob_agecat_mpact > > . checkpop > > Total pop: 332,455,972 > Observations: 47,267,047 > Missing: 0 > > . collapse (sum) pop, by(statefips countyfips agecat_mpact sexcat > racecat iprcat_mpact ip >> rcat coverage groupsize) > > . checkpop > > Total pop: 332,455,972 > Observations: 36,351,520 > Missing: 0 > > > ************** RUN B ************* > . merge m:m statefips agecat_census using "ABCD.dta" > > Result # of obs. > ----------------------------------------- > not matched 0 > matched 47,267,047 (_merge==3) > ----------------------------------------- > > . assert _merge==3 > > . drop _merge > > . egen tot_pop=sum(pop), by(statefips countyfips agecat_census sexcat > racecat iprcat_mpac >> t iprcat coverage groupsize) > > . checkpop > > Total pop: 347,095,179 > Observations: 47,267,047 > Missing: 0 > > . rename pop oldpop > > . gen pop=tot_pop*prob_agecat_mpact > > . checkpop > > Total pop: 332,455,928 > Observations: 47,267,047 > Missing: 0 > > . collapse (sum) pop, by(statefips countyfips agecat_mpact sexcat > racecat iprcat_mpact ip >> rcat coverage groupsize) > > . checkpop > > Total pop: 332,455,928 > Observations: 36,351,515 > Missing: 0 > * > * 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/ * * 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/