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st: RE: computing days
Nick Cox <email@example.com>
st: RE: computing days
Wed, 16 Mar 2011 16:56:25 +0000
SJ-7-3 pr0033 . . . . . . . . . . . . . . Stata tip 51: Events in intervals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q3/07 SJ 7(3):440--443 (no commands)
tip for counting or summarizing irregularly spaced
events in intervals
That is accessible to all via the Stata Journal website.
I have a large set of events (debt ratings issued by rating agencies on debt issued by one company) for which I do have exact dates. Prior to each rating some banks have issued recommendations on the company like Buy or Sell. I do have exact dates for these as well.
Ratings are issued independently by multiple agencies. Ratings are issued on a large number of companies and each is identified by an ID. I want to calculate how many recommendations have been issued before each rating and the average number of days before the rating for all recommendations.
My dataset looks like this (for just one company ID):
RatingEvent date RatingDate date120 date90 date60
1 17jul2002 17jul2002 19mar2002 18apr2002 18may2002
1 06aug2002 06aug2002 08apr2002 08may2002 07jun2002
The first column identifies the rating issuance. The second column is identifies the dates when recommendations AND ratings have been issued. The third column reports only issuing dates for the rating (of course the info is identical to that reported in column 2. It's redundant). The 4th to 6th columns identify the beginning date of the 3 relevant windows: 120, 90 and 60 days, all ending, obviously on the rating issuance date.
Basically I would like to create a variable that tells me that, for instance, for the rating issued on 7/17/2002 I have 14 recommendations that have been issued on average 52 days before the rating (I have manually computed these data) if I'm looking at the 120days window. A second variable should give me the same info on the 90 days window and so on for the 60 days.
An additional problem is that the last row indicates that a few days after the first rating a second rating has been issued (possibly but not necessarily by a different agency). In such a case a number of record would be in common but some would not. Since I can identify ex-post through additional identifiers the company, the agency etc I just need to have these two infos: count and mean days of recommendations before each rating.
I've been struggling for days. I hope you can help me.
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