st: RE: what command to keep firms-years with multiple occurrence of only one type of events

[Joe Canner <jcanner1@jhmi.edu>]

Nahla.

If your Event variable is numeric, this should work:

. bys Firm Year: egen mn=mean(Event)
. bys Firm Year: egen sd=sd(Event)
. keep if mn==3 & sd==0

This is, admittedly, a little unconventional, but should be pretty efficient.

Regards,
Joe Canner
Johns Hopkins University School of Medicine

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nahla Betelmal
Sent: Friday, September 27, 2013 4:43 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: what command to keep firms-years with multiple occurrence of only one type of events

Dear Statalist members,

It would be great if you can let me know what command I can use to keep firms-years with multiple occurrence of only one type of events in my data.

I have firms-years-events data set. A firm can have multiple entries for the same year if it undertakes certain corporate events . I coded the events as 1,2,3, 4. For example the data looks like this


Firm   Year    Event
A        1994       2
A        1994       3
A        1994       3
A        1995       1
A         1995      3
A         1996       2
A         1996       4
A         1996       3
A          1997       3
A           1997      3
A           1998       1
A            1998       1
B
..


I am only interested in studying firm-years where  only event 3 was undertaken (i.e. keep both entries for year 1997 only). In other words, I want to drop firm years where there are a mix of events shown as multiple entries/observations ( years 1994, 1995, 1996) and multiple unique occurrence of event other than 3 (year 1998).

I understand that I can do it on two stages, first drop  firm-years with mix events, then second stage drop years with unique events other than 3.

the problem that I  don't know what command should I use to do the first stage ( drop firms-years with multiple entries of multiple events).

Thank you in advance, I highly appreciate your kind help

Nahla Betelmal
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/