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| From | Richard Williams <richardwilliams.ndu@gmail.com> |
| To | statalist@hsphsun2.harvard.edu, "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |
| Subject | Re: st: upper limit on fweights? overflowing into missing values? |
| Date | Mon, 29 Jul 2013 08:53:39 -0500 |
Just to sum up my current thinking/guesses on this: * the maximum number of observations in Stata is 2,147,483,647 * Nonetheless, fweighted data sets can have more observations than that* However, not all routines will work when the fweighted data has more than 2,147,483,647 cases. You can do some simple descriptive things, but you can't do more complicated things like regression or correlations. * As to why that is, I am guessing that some routines have the 2,147,483,647 limit hardcoded in. Or, maybe there just isn't enough precision to handle calculations when the N is larger than that. * Given that most people don't have more than 2,147,483,647 cases (and even if they did, their computer memory couldn't handle them) StataCorp probably hasn't spent a lot of time worrying about this. * Still, an added sentence or two in the fweights documentation or elsewhere warning about limits might be a good idea.
I am curious what the original author is doing that requires analyzing 4 billion+ cases. Some sort of genetic research maybe? I've certainly never heard of any kind of Survey research having an N that large.
At 06:53 PM 7/28/2013, Nick Cox wrote:
This is interesting, but in principle I don't see that Stata's limit on # of observations has any bearing on how big frequency weights can be. I can imagine people wanting to use frequency weights to subvert the limit on number of observations. A different point is that if there is a limit on how big weights can be it should be documented e.g. at -help limits-. Nick njcoxstata@gmail.com On 29 July 2013 00:46, Richard Williams <richardwilliams.ndu@gmail.com> wrote:> According to -help limits-, the maximum number of observations is 2,147,483,647. Your weights give you more than 4 billion cases, well above that. Further, the help also says that this is a theoretical maximum; memory availability will certainly impose a smaller maximum.>> On my computer, I specified [fw = 1073741823] on the pwcorr command and it ran. Then I specified [fw = 1073741824] and it did not run. These numbers put you just below and just above the maximum number of cases that Stata allows.>> So in short, it appears that your fweighted cases can't exceed the 2 billion+ that Stata allows, and memory restrictions may hold you to even less than that.>> Also, you probably need to specify that the fweight variable is type long, e.g.> > input y x long fw > > Sent from my iPad > > On Jul 27, 2013, at 12:36 PM, László Sándor <sandorl@gmail.com> wrote: > >> Hi, >> If you care, here is an example that silently produces missing values. >> I notified Stata Support. >> >> input y x fw >> 2 1 2147483621 >> 1 2 2147483621 >> end >> de >> pwcorr y x [fw=fw] >> exit >> >> Thanks, >> >> Laszlo >> >> On Sun, Jul 21, 2013 at 5:08 PM, Nick Cox <njcoxstata@gmail.com> wrote: >>> I'd suggest documenting your problems with a reproducible example and >>> sending Stata tech support. >>> >>> >>> Nick >>> njcoxstata@gmail.com >>> >>> >>> On 21 July 2013 21:55, László Sándor <sandorl@gmail.com> wrote: >>>> Hi, >>>> in Stata/MP 12.1 I am getting missing values with using -pwcorr- with >>>> -fweights- though the feature works fine with other data or if I scale >>>> my weights down. Is it possible to simply have too large fweights, >>>> e.g. if they cannot be of type -long- anymore? >>>> >>>> If so, why doesn't Stata warn me about this? >>>> >>>> I vaguely remember some Statalist of Stata blog discussion of this, >>>> but I could not even Google it up, and Stata still did not warn me? >>>> >>>> Actually, why didn't Stata complain that I did not have integer >>>> fweights if obviously the variable wasn't of type byte, int or long? >>>> >>>> Thanks, >>>> >>>> Laszlo >>>> >>>> * >>>> * 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/ >> >> * >> * 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/ * * 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/
------------------------------------------- Richard Williams, Notre Dame Dept of Sociology OFFICE: (574)631-6668, (574)631-6463 HOME: (574)289-5227 EMAIL: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * 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/