Year group categories from dates

[Girish Venkataraman]

I am trying to generate two decade groups "2010 or earlier" and "2011 and above" for dates of CLL diagnosis and I am not getting the right answers in date and floor functions.

This code clearly does not seem right

gen timeperiod = 0 if clldate < 1/1/2011

* Example generated by -dataex-. For more info, type help dataex
clear
input float clldate
17209
19045
20590
20529
    .
17016
20996
17532
17167
17532
19788
15857
20083
15675
17468
17532
18628
16071
19792
17532
11688
19449
17532
10227
16802
17532
17167
 9132
19484
19359
15706
16802
19502
17532
18749
17167
18263
    .
10958
15706
14610
16802
    .
17843
10593
15522
16802
16802
    .
14245
    .
    .
16071
16887
14976
16539
13515
16713
15264
    .
14335
15341
10227
    .
13515
14976
15219
13149
15111
14610
13515
12419
    .
14610
13635
    .
16204
20369
17714
18049
18597
17563
21608
17785
19175
21933
20675
14031
19632
19024
19237
21117
22103
21011
19715
20118
20292
16496
16802
21094
end
format %td clldate

[William Lisowski]

Perhaps this code applied to your example data will start you in a useful direction.

. generate timeperiod = clldate > td(31/12/2010) if clldate!=.
(10 missing values generated)

. tabstat clldate, statistics(min max) by(timeperiod) missing format(%td)

Summary for variables: clldate
Group variable: timeperiod 

timeperiod |       Min       Max
-----------+--------------------
         0 | 01jan1985 01dec2010
         1 | 01jan2011 07jul2020
         . |         .         .
-----------+--------------------
     Total | 01jan1985 07jul2020
--------------------------------

Stata's "date and time" variables are complicated and there is a lot to learn. If you have not already read the very detailed Chapter 24 (Working with dates and times) of the Stata User's Guide PDF, do so now. If you have, it's time for a refresher. After that, the help datetime documentation will usually be enough to point the way. You can't remember everything; even the most experienced users end up referring to the help datetime documentation or back to the manual for details. But at least you will get a good understanding of the basics and the underlying principles. An investment of time that will be amply repaid.

All Stata manuals are included as PDFs in the Stata installation and are accessible from within Stata - for example, through the PDF Documentation section of Stata's Help menu.

[Girish Venkataraman]

Thanks much, William. Will go through help datetime. I just learnt about the MD20Y mask yesterday. Another nice thing for today from you.