Listing cohorts: Number of firm-year observations

[Mabel Costa]

Hello Guys,

My sample period is 1976 to 2016 (fyear in the attached dta file and gvkey is the firm id)
Based on the paper by Srivastava (2014, Why have measures of earnings quality changed over time?) I am trying to prepare a table similar to Table 1: The number of firm-year observations from the successive listing cohorts in each year. For my case firms prior to 1980 will be seasoned firms with new firms for 1980s wave, 1990s wave and 2000s wave

The table will look like as following (based on full sample)

Fiscal year	Total number of firms	Seasoned firms (firms from 1970s)	1980’s wave	1990s wave	2000s wave
1980	4013	3832	181
1981	4010	3543	467
1982	3946	3252	694
1983	4165	2964	1201
1984	4204	2589	1615
1985	4161	2199	1962
1986	4317	1839	2478
1987	4440	1469	2971
1988	4392	1036	3356
1989	4314	638	3676
1990	4339			352
1991	4366			680
1992	4471			1061
1993	4757			1601
1994	5034			2172
1995	5324			2816
1996	5863			3760
1997	5860			4265
1998	5536			4547
1999	5425			5070
2000	5099				403
2001	4816				738
2002	4710				1028
2003	4706				1391

Where 1980s wave column for the year 1980 is the new firms of 1980. For year 1981 is the summation of new firms in 1980 and 1981 and so forth. What I am unable to do when I move to year 1990 and onward I can’t identify how many of 1970s firms still exists and how many 1980s firms still exists in 1990, 1991 and so on.

I have attached partial sample Stata dta file. Your help will be highly appreciated.

Regards

[Phil Bromiley]

Please read the FAQ on asking questions. You are advised to provide Stata code in code delimiters, readable Stata output, and sample data using dataex. Many of us will not open files from people we don't know due to concerns about viruses.

If you have information on the existence of the firm in each year, you can easily make an indicator showing the firm existed in 1970 or whatever. You can use bysort gvkey: egen with either means or totals to paste that value across all observations for that firm. Then you can simply compare with the firm existed in 1970. Once you have identified the group, you can easily use table or summary to count observations.