Calculate the asset growth rate for quarterly panel data

[Cong Gu]

Dear Statalists,

My main target here is to calculate the asset growth rate over the last quarter for a specific firm, the data is quarterly panel, for example:

firm_id	year	quarter	assets
37	1997	1	58891
37	1997	2	57317
37	1997	3	57993
37	1997	4	60834
37	1998	1	61299
37	1998	2	61260
37	1998	3	60447
37	1998	4	61351
37	1999	1	61655
37	1999	2	62144
37	1999	3	63308
37	1999	4	63963
242	1997	1	19925
242	1997	2	20764
242	1997	3	19845
242	1997	4	20676
242	1998	1	20663
242	1998	2	20898
242	1998	3	20761
242	1998	4	21914
242	1999	1	21404
242	1999	2	21404
242	1999	3	21824
242	1999	4	22885
279	1997	1	89224
279	1997	2	88541
279	1997	3	89206
279	1997	4	87353
279	1998	1	86906
279	1998	2	86241
279	1998	3	88516
279	1998	4	90896
279	1999	1	90206
279	1999	2	92940
279	1999	3	92302
279	1999	4	93211

firm_id represents a unique firm identifier, so, is "egen" function appropriate here?

All I need is to generate another variable named as assets_growth_rate=(Assets in Quarter_n+1-Assets in Quarter_n)/Assets in Quarter_n.

Many thanks for your help in advance.

With kind regards,

Cong

[Clyde Schechter]

Probably the simplest way to do this is:

gen quarterly_date = quarterly(string(year)+"q"+string(quarter), "YQ")
xtset firm_id quarterly_date
gen assets_growth_rate = (F.assets-assets)/assets

Not only is the code compact, but it will automatically generate missing values where there are gaps in the series of quarters.

[Cong Gu]

Many thanks!!really appreciate your help!!

[Nick Cox]

Note also the yq() function.