Re: st: Generating days eligible when eligibility changes over time

[Nick Cox <njcoxstata@gmail.com>]

This is an interesting problem.

I haven't tried understanding your code exactly, but note that you
seem to be confusing the -if- command and the -if- qualifier, perhaps
due to some previous or concurrent life as a SAS user.

0. I don't think I understood about the "survey date" and when that was.

1. In your sample data, birthdays often look off, so that (e.g.) the
first two individuals capriciously celebrate their birthdays a day
earlier than usual in some or all cases.

06sep1995 05sep2002 05sep2004 05sep2006
06dec1994 05dec2001 06dec2003 05dec2005

Birthdays in my view are better calculated by Stata. I know of one
predictable problem and presume that people born on 29 February are
deemed to celebrate their birthday on 28 February when it's not a leap
year.

2. The exact rule could be that eligibility ends (a) on a particular
birthday or (b) on the day before, but I'll let you worry about that
and add or subtract 1 according to whether code is correct or off.

This code gives some technique that may help.

clear
input str9 birthday
01jan1950
01jan1995
01apr1995
01jan1997
01apr1999
31dec1991
end

gen dbirthday = date(birthday, "DMY")

local start1 = date("01jan1998", "DMY")
local limit1 = 7
local start2 = date("01apr2003", "DMY")
local limit2 = 9
local start3 = date("01jan2004", "DMY")
local limit3 = 11
local start4 = date("01jan2005", "DMY")
local limit4 = 14
local start5 = date("01jan2008", "DMY")
local limit5 = 15
local start6 = date("01jan2010", "DMY")
local limit6 = 18

gen limitdate = .
gen eligible = 0

qui forval j = 1/6 {
    replace limitdate = mdy(month(dbirthday), day(dbirthday),
year(dbirthday) + `limit`j'')
    replace limitdate = mdy(2, 28, year(dbirthday)) if
missing(limitdate) & !missing(dbirthday)
    replace eligible = eligible + max(0, limitdate - `start`j'')
}

list , sep(0)

I would always recommend working with a test dataset for which the
correct answers can be calculated independently.

Nick
njcoxstata@gmail.com


On 7 March 2014 00:19, Brill, Robert <robertbrill@austin.utexas.edu> wrote:
> Hi Listers,
>
> Iım working on a project in which I am generating an ³intended dosage²
> variable equal to the number of days that a person was
> eligible for a cash grant program.  In short, Iıd like to know how many
> days a child was eligible for the program between the program start and
> the survey date. Eligibility is based on being under an age cutoff. The
> government in question, however, changed the eligibility age 4 times over
> the course of the period of interest (1998-2010).
>
> The program began on 01jan1998, and was available to children under 7. On
> 01apr2003 the eligibility was increased to 9, on  01jan2004 to 11, on
> 01jan2005 to 14, on 01jan2008 to 15, and on 01jan2010 to 18.
>
> Therefore, if an individual turned 7 after the first eligibility change
> occurred, she was eligible from the beginning of the program in 1998 until
> the date of the survey in 2010. However, if she turned 7 before the
> change, she is only eligible for the number of days from the beginning of
> the program until the date she turned 7. Itıs also possible  that a
> different child with a different birthday would fluctuate back and forth
> in eligibility as the changes occurred (depending on her birthday,
> obviously).
>
> To generalize to all cases, Iıve considered generating a dose variable for
> each of the periods (1998-2003, 2003-2004, 2004-2005, 2005-2008, and
> 2008-2010) which uses if and if else statements to take all of the types
> of cases into account when subtracting birthdays and eligibility change
> days etc., or, alternatively, generating a couple hundred month indicators
> (or a few thousand days) that are 1 if an individual was eligible in that
> month (or day), then calculating the row total to tell me the number of
> months (or days) eligible.
>
> However, Iıd much prefer to have a fully accurate measure to the day, and
> it seems a bit too crazy to generate all of those indicators when thereıs
> likely another way, but I havenıt been able to think my way out of my
> current funk.
>
> The variable ³birthday² is a %td formatted individual birthday. ³turned7²
> is the date that the individual turned 7 (and exists for each age,
> turned9, etc.).
>
> Right now, the code looks like:
>
>
> ** Input some example data
> input str9 birthday str9 turned7 str9 turned9 str9 turned11
> 06sep1995 05sep2002 05sep2004 05sep2006
> 06dec1994 05dec2001 06dec2003 05dec2005
> 23oct1995 22oct2002 22oct2004 22oct2006
> 01dec1994 30nov2001 01dec2003 30nov2005
> 08sep1994 07sep2001 08sep2003 07sep2005
> 26jun1995 25jun2002 25jun2004 25jun2006
> 10nov1995 09nov2002 09nov2004 09nov2006
> 12feb1994 11feb2001 12feb2003 11feb2005
> 16nov1995 15nov2002 15nov2004 15nov2006
> 10feb1994 09feb2001 10feb2003 09feb2005
> 01sep1994 31aug2001 01sep2003 31aug2005
> 26oct1994 25oct2001 26oct2003 25oct2005
> 21nov1994 20nov2001 21nov2003 20nov2005
> 03nov1994 02nov2001 03nov2003 02nov2005
> 10mar1994 09mar2001 10mar2003 09mar2005
> 31oct1994 30oct2001 31oct2003 30oct2005
> 08aug1994 07aug2001 08aug2003 07aug2005
> 21dec1994 20dec2001 21dec2003 20dec2005
> 10may1994 09may2001 10may2003 09may2005
> 19apr1994 18apr2001 19apr2003 18apr2005
> 05nov1994 04nov2001 05nov2003 04nov2005
> 18dec1995 17dec2002 17dec2004 17dec2006
> 24may1995 23may2002 23may2004 23may2006
> 15aug1994 14aug2001 15aug2003 14aug2005
> 05apr1995 04apr2002 04apr2004 04apr2006
> end
>
> ** format inputted data
> foreach v of varlist *{
> g td`v'=date(`v', "DMY")
> drop `v'
> rename td`v' `v'
> format `v' %td
> }
>
>
> **generate dose by period vars
>
> forval i=1/5 {
>     g p`i'dose=.
>     }
>
>
> ** use a bunch of if/else statements to generate dosage by period to be
> summed later
> foreach e in 7  {
>         local start "mdy(01,01,1998)"
>         local p1 "mdy(04,01,2003)"
>         local p2 "mdy(01,01,2004)"
>         local p3 "mdy(01,01,2005)"
>         local p4 "mdy(01,01,2008)"
>         local p5 "mdy(01,01,2010)"
>
>         if turned7>`p1' {
>             replace p1dose=`p1'-birthday
>         }
>
>         else if turned7<`p1' & birthday>`start' {
>             replace p1dose=turned7-birthday
>         }
>
>         else if turned7<`p1' & birthday<`start' {
>             replace p1dose=turned7-`start'
>         }
>
>         if turned9>`p2ı & turned7>`p1ı {
>             replace p2dose=`p2ı-`p1ı
>         }
>
>         else if turned9<`p2ı & turned9>`p1ı {
>             replace p2dose=turned9-`p1ı
>         }
> ** etc etc etc
>
>
>
> Or alternatively, the code could look like
>
>
> forval m=1/12 {
>
> forval y=1998/2012 {
>
>     if `yı<2003 { //this has a problem because of the april thing but you
> get the idea
>         g drop`mı`yı=(((mdy(`mı,01,`yı)-birthday)/365.25)<7)
>         }
>
>     else if  `yı >2002 & `yı<2005 {
> ** etc etc etc
> }
>
>
>
> While Iım not entirely opposed to doing one of these ways, Iım wondering
> if there is some obvious or less-obvious way to go through this in a more
> efficient way or that perhaps requires less opaque code.
>
> Any hints, tips, or tricks are very welcome and will be received with
> extreme gratitude, Iıve been banging my head against a wall on this for a
> while now and would love to hear new perspectives on the problem.
>
>
> Thanks greatly for your time, and for all the great help that Iıve gotten
> in the past by searching the archive.

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