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Home » Countries » India » Median Age at Any Event (Stata Code to calculate median age at any specific event (such as first marriage, first birth etc). This code will give you the final answers that will match with NFHS reports. (India-NFHS))
Median Age at Any Event [message #29806] Wed, 07 August 2024 12:40 Go to next message
crabyou is currently offline  crabyou
Messages: 1
Registered: August 2024
Member
Since I had to spend a day to finally figure out how the median age variables on NFHS reports are calculated, here is the code for anyone trying the same. I do not claim originality, I have taken snippets of code from multiple sources to customise this code. I illustrate the code below with NFHS-5 data and reports.

program define calc_median_age

** Source: https://userforum.dhsprogram.com/index.php?t=msg&goto=12912&&srch=svyset+individual+data#msg_12912

replace age=99 if age==. | age==0 // age is any age var of interest. ideally these should be coded missing but the values in NFHS reports will differ slightly without this recoding

summarize age [fweight=v005], detail

scalar sp50=r(p50)

gen dummy=0 
replace dummy=1 if age<sp50 


summarize dummy [fweight=v005]
scalar sL=r(mean)

replace dummy=0 
replace dummy=1 if age<=sp50 

summarize dummy [fweight=v005]
scalar sU=r(mean)

drop dummy

scalar smedian=round(sp50+(.5-sL)/(sU-sL),.01)
scalar list sp50 sL sU smedian

* warning if sL and sU are miscalculated
if sL>.5 | sU<.5 {
display in red "ERROR IN CALCULATION OF L AND/OR U"
}

drop age
end

*******************************************************
*******************************************************
*******************************************************
*******************************************************
*******************************************************
*******************************************************
* EXECUTION BEGINS HERE

* sp50 is the integer-valued median produced by summarize, detail;
*   what we need is an interpolated or fractional value of the median.

* In the program, "age" is reset as age at first any event of interest.

* sL and sU are the cumulative values of the distribution that straddle the integer-valued median

set maxvar 10000
use "NFHS/IAIR7EDT/IAIR7EFL.DTA", clear // individual level women data

************************* Create Variables ***********************************

**** Age at first marriage 
replace s308c=. if s308c==9998 | s308c==9997 // inconsistent ( coded as 9997 ) or don't know ( coded as 9998 )
replace s309=. if s309==98 // dont know is coded as 98 

**Source: suggested method for calculating age at marriage https://userforum.dhsprogram.com/index.php?t=msg&goto=14267&S=Google#:~:text=Can%20anyone%20illustrate%20this%20variable%3F&text=*Using%20this%20syntax%2C%20it%20has,before%2018%20years%20of%20age.

gen afm= int((s308c - v011) / 12)
replace afm=s309 if afm==.

la var afm "Age at First Marriage"

**** Age at first birth
gen afb= int((v211-v011)/12)
la var afb "Age at First Birth"


************************** Replicate Numbers on Report *************************
****** Source: https://dhsprogram.com/pubs/pdf/FR375/FR375.pdf
***** Median age at first marriage is 19.2 years among women age 20-49 - Page 208
preserve
gen age=afm

keep if v013!=1 // 20-49 olds

calc_median_age
scalar median_ans=smedian
scalar list median_ans
restore

***** Median age at first birth among women age 25-49 in India is 21.2 years - Page 114
preserve
gen age=afb

keep if v013!=1 & v013!=2 // 25-49 olds

calc_median_age
scalar median_ans=smedian
scalar list median_ans
restore


For calculating median age at any event for men, replace the weights (v005) with men's sample weights. I have also added the relevant links I had referred to.
Re: Median Age at Any Event [message #29809 is a reply to message #29806] Wed, 07 August 2024 14:01 Go to previous message
Bridgette-DHS is currently offline  Bridgette-DHS
Messages: 3190
Registered: February 2013
Senior Member

Following is a response from Senior DHS staff member, Tom Pullum:

Glad you were able to locate this simple procedure. I wrote it several years ago and it is now included (with some variations) in the GitHub code wherever medians are required.
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