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From | Gwinyai Masukume <parturitions@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: how does one automatically calculate the age in years by subtracting the system date from the date of birth? |
Date | Sun, 10 Mar 2013 17:22:00 +0200 |
Many thanks Rebecca for the very helpful and clear step by step explanation. Removing the following from your example seems to generate the same results? local sd = date("`c(current_date)'","DMY") set seed `sd' Would the above coding mean the seed would change daily? Would anyone know if there’s a difference between %d and %td? /*** full example modified ***/ version 12 clear set obs 5 * local sd = date("`c(current_date)'","DMY") * set seed `sd' scalar start = mdy(1,1,1964) scalar end = mdy(12,31,1999) gen date_of_birth = int(start+(end-start)*runiform()) gen today_date=date("`c(current_date)'","DMY") gen age = round((today_date - date_of_birth)/365.25,0.1) gen age2 = int((today_date - date_of_birth)/365.25) format date_of_birth today_date %td list, noobs /*** end ***/ Thanks again. Regards G On 3/10/13, Rebecca Pope <rebecca.a.pope@gmail.com> wrote: > A correction first. > > gen month_dob=int(1+(13-1)*runiform()) > gen day_dob=int(1+(32-1)*runiform()) > gen year_dob=int(1964+(1999-1964)*runiform()) > gen date_of_birth=mdy(month_dob, day_dob, year_dob) > > has the potential to produce an error, albeit with a small > probability. Since you are drawing months and days separately, you can > draw nonsensical combinations like 2/30. A better method is to draw > randomly over the range of dates that you want. > > scalar start = mdy(1,1,1964) > scalar end = mdy(12,31,1999) > gen date_of_birth = int(start+(end-start)*runiform()) > * the two -scalar- assignments can be skipped & placed directly in > date_of_birth, but I find this clearer (i.e. just style) > > You also say: >> I’m encountering some problems subtracting these two >> dates. Could this be due to date formats i.e. month day year (MDY) >> versus day month year (DMY). Or it could be due to one date being an >> integer and the other a string? Or it's something else? > > To refer to the _content_ of c(current_date), you must treat it as a > macro: `c(current_date)'. Then use it in the -date()- function to > convert to a date value, because yes, you must have two numeric values > in order to subtract. > > gen today_date=date("`c(current_date)'","DMY") > > Finally: >> Theoretically subtracting the today_date from date_of_birth should >> give the age, > > Not so. You should subtract date_of_birth from today_date. This gives > you the difference in days from which you can calculate age in > (fractional) years. If you don't want to change age until the person > has had a birthday, then use the -int()- function. > > gen age = round((today_date - date_of_birth)/365.25,0.1) > gen age2 = int((today_date - date_of_birth)/365.25) > > /*** full example ***/ > version 12 > clear > set obs 5 > local sd = date("`c(current_date)'","DMY") > set seed `sd' > > scalar start = mdy(1,1,1964) > scalar end = mdy(12,31,1999) > gen date_of_birth = int(start+(end-start)*runiform()) > > gen today_date=date("`c(current_date)'","DMY") > > gen age = round((today_date - date_of_birth)/365.25,0.1) > gen age2 = int((today_date - date_of_birth)/365.25) > > format date_of_birth today_date %td > list, noobs > /*** end ***/ > > Output: > date_of~h today_d~e age age2 > ------------------------------------- > 08sep1983 10mar2013 29.5 29 > 15jul1965 10mar2013 47.7 47 > 11dec1970 10mar2013 42.2 42 > 09jan1978 10mar2013 35.2 35 > 15oct1987 10mar2013 25.4 25 > > Regards, > Rebecca > > * > * 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/