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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: cumulative moving sum when there are repeated date values |

Date |
Thu, 5 Feb 2009 10:49:42 -0000 |

This is discussed in 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 Nick n.j.cox@durham.ac.uk Padma Rao Sahib I have a panel dataset of acquisition attempts made by firms in which I would like to calculate the cumulative number of acquisitions a firm completes in the past 5 years prior to the current acquisition. Firms enter the dataset if they make an acquisition attempt but as some acquisitions are later abandoned, I have an acquisition completion dummy "acdum" that is 1 if the acquisition is completed, 0 otherwise" . My data looks like this: Acdum is the Acquisition completion dummy. Firmid Date Acdum Cumulative Shell 24 Jan 1993 1 0 Shell 1 Dec 1995 0 1 Shell 3 Aug 1996 1 1 Shell 3 Aug 1996 1 2 Mittal Steel 3 Jan 1993 1 0 Mittal Steel 4 March 2000 1 0 Mittal Steel 5 April 2001 1 1 I would like to count the cumulative number of acquisitions made by the firm in the past 5 years prior to the current acquisition (even if they occured in the same year ). By searching Statalist, I found a solution using " tssmooth, egen and a filter. However, these solutions involving tsseting the data and as it can be seen from the example above, I have firms that sometimes announce two acquisitions as being completed on the same day (and I don't have any finer time details like hours etc.) to tsset the data properly. As a result I get an error message saying that I have repeated time values within my panel. The actual ordering of acquisitions that occur on the same day does not matter, I simply need to sum up the number of acquisitions prior to the current one as long as they occurred in a 5 year interval, and it is OK if the ones on the same day are off by one acquisition. I tried something like this: bysort firmid (date):gen prevacq = sum(acdum) by firmid: gen prevacq5 = prevacq - prevacq[_n-4) (also borrowed and adapted from a solution to a related question on statalist) but this does not quite work and seems to cap the number of previous acquisitions at 4. Out of desperation, I thought of manually adding a day to the date announced as it is the year that is important but there are too many observations for this to be feasible...I think I need a loop of some sort but my STATA loop knowledge is somewhat deficient.. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: cumulative moving sum when there are repeated date values***From:*"P. Rao Sahib" <p.rao.sahib@rug.nl>

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