How do I generate age category? My PATIENT_YOB is given as 01jan1956 and I want to get exact age

Question

I'm trying to use the following code but it gives error

 01jan1986 
05jan2001 
07mar1983 
and so on I need to get the exact age of them
gen agecat=1
if age 0-20==1
if age 21-40==2
if age 41-60==3
if age 61-64==4```

Answer 1

Here's one way:

gen age_cat = cond(age <= 20, 1, cond(age <= 40, 2, cond(age <= 60, 3, cond(age <= 64, 4, .))))

You might also want to look into egen, cut, see help egen.

Answer 2

To build off of Wouter's answer, you could do something like this to calculate the age to the tenth of a year:

clear
set obs 12
set seed 12352

global today = date("18Jun2021", "DMY")

* Sample Data
gen dob = runiformint(0,17000) // random Dates
format dob %td

* Create Age
gen age = round((ym(year(${today}),month(${today})) - ym(year(dob), month(dob)))/ 12,0.1)

* Correct age if dob in current month, but after today's date
replace age = age - 0.1 if (month(${today}) == month(dob)) & (day(dob) > day(${today}))

* age category
gen age_cat = cond(age <= 20, 1, cond(age <= 40, 2, cond(age <= 60, 3, cond(age <= 64, 4, .))))

The penultimate step is important as it decrements the age if their DOB is in the same month as the comparison date but has yet to be realised.

     +----------------------------+
     |       dob    age   age_cat |
     |----------------------------|
  1. | 30jan2004   17.4         1 |
  2. | 14aug1998   22.8         2 |
  3. | 06aug1998   22.8         2 |
  4. | 31aug1994   26.8         2 |
  5. | 27mar1990   31.3         2 |
     |----------------------------|
  6. | 12jun1968     53         3 |
  7. | 05may1964   57.1         3 |
  8. | 06aug1994   26.8         2 |
  9. | 21jun1989   31.9         2 |
 10. | 10aug1984   36.8         2 |
     |----------------------------|
 11. | 22oct2001   19.7         1 |
 12. | 03may1972   49.1         3 |
     +----------------------------+

Note that the decimal is just approximate as it uses the month of the birthday and not the actual date.

Answer 3

You got some good advice in other answers, but this can be as simple as you want.

Consider this example, noting that presenting data as code we can run is a really helpful detail.

* Example generated by -dataex-. For more info, type help dataex
clear
input str9 sdate float dob
"01jan1986"  9497
"05jan2001" 14980
"07mar1983"  8466
end
format %td dob

The age at end 2020 is just 2020 minus the year people were born. Use any other year if it makes more sense.

. gen age = 2020 - year(dob)

. l

     +-----------------------------+
     |     sdate         dob   age |
     |-----------------------------|
  1. | 01jan1986   01jan1986    34 |
  2. | 05jan2001   05jan2001    19 |
  3. | 07mar1983   07mar1983    37 |
     +-----------------------------+

For 20 year bins, why not make them self-describing. Thus with this code, 20, 40 etc. are the upper limit of each bin. (You might need to tweak that if you have children under 1 year old in your data.)

. gen age2 = 20 * ceil(age/20)

. l

     +------------------------------------+
     |     sdate         dob   age   age2 |
     |------------------------------------|
  1. | 01jan1986   01jan1986    34     40 |
  2. | 05jan2001   05jan2001    19     20 |
  3. | 07mar1983   07mar1983    37     40 |
     +------------------------------------+

This paper is a review of rounding and binning using Stata.