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From |
"Diana Beketova" <diana.beketova@gmx.de> |

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

Subject |
AW: AW: st: Merge Panel Datasets |

Date |
Mon, 20 Jun 2011 03:41:58 +0200 |

Hello Phil, thank you very much for your time and an extended answer to my question. I have to apologize, if maybe my problems seem 'beginner-level' for you, but I am using Stata seriously since quite a short time now and am trying to catch up quickly in order to be on your level :-) This is totally true that I first had to create 'total foreign ownership' and 'total domestic ownership' in order to make one observation line out of many. But I first wanted just to try to merge both data files, so I can see if this merge can be successful at all and where are my week points to work on. I had an idea about building year clusters because I have a range of years 2002-2010. So I can build 3x3 year clusters: 2002-2004, 2005-2007, 2008-2010. Within each of these years I can generate new variables for Total Assets and Oper. Revenue that will be averages of Total Assets and Oper. Revenue within this cluster. Because ownership is so oddly distributed, there is a high probability that there will be only one observation per year cluster. At the end I would use Heckman correction method in order to correct for selection bias. Or also Tobit-model for censored variables. Do you think, this methodology could be reasonable to use? Otherwise, I don?t know how to match these to files. I have to say that data comes from an emerging market and is very biased and incomplete. Maybe you know further ways how to deal with the bias problem? Best wishes, Diana -----Ursprüngliche Nachricht----- Von: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Phil Schumm Gesendet: Sunday, June 19, 2011 5:56 PM An: statalist@hsphsun2.harvard.edu Betreff: Re: AW: st: Merge Panel Datasets On Jun 19, 2011, at 1:28 AM, Diana Beketova wrote: > You describe everything right. Indeed, I have yearly total assets > and revenues in the master data and multiple observations per year > about firm ownership structure in the using-data. I have to analyze > the impact of foreign ownership on firm value/profitability > afterwards. The dataset is very big and also causes some problems > because I am limited to 1GB memory on my computer. The goal is also > to find out which companies survived best during the crisis, what > type of foreign owner had the most positive effect on firm > performance etc. I made the merge again using 1:m-option and you can > see my results below. I just can't believe that out of almost 1.9 > million observations only 451 match. > > merge 1:m ID_NUMBER YEAR using file2 > ID_NUMBER was str15 now str16 > > Result # of obs. > ----------------------------------------- > not matched 1,894,248 > from master 387,108 (_merge==1) > from using 1,507,140 (_merge==2) > > matched 451 (_merge==3) > ----------------------------------------- > > At the end I want to have a panel that contains all observations > over years, so I can run all the needed regressions etc. Do you > think it is somehow possible? I agree that this seems odd -- the only way to find out what is going on is to inspect some of the "master only" and "using only" observations (I would suggest doing this for a few, specific firms). Assuming you don't see any problems, then it simply means that for most firms and/or most years, you either have data on assets and revenue *or* data on ownership, but not both. If that's true, then you need to think about how you're going to handle that in your analysis (e.g., by estimating values for the interim years, or by using a model that does not require concurrent observations on your measures). I'm guessing that you're going to need to do some work with your ownership data before you can use them in a model. For example, you may need to compute measures like "total percent foreign ownership," "percent owned by specific countries," etc. If so, then you probably want to do these calculations before merging. Finally, if you're running up against memory constraints (and can't buy/borrow more memory or move to another machine), then make sure you are storing and using your data in the most memory-efficient way possible. For example, eliminate any unnecessary variables (e.g., the observation number variable in your example), and make sure you are storing everything in the most efficient way possible (e.g., store variables such as country code as numeric with value labels, and use - compress-). Also, as I noted in my previous email, your current merge result (with multiple observations per firm for each year) is very inefficient, because information on assets and revenue for a given year is duplicated. If your analysis will ultimately be based on a file with only one observation per firm per year, then you should modify your second file accordingly before merging it on. -- Phil * * 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/ ----- eMail ist virenfrei. Von AVG überprüft - www.avg.de Version: 10.0.1382 / Virendatenbank: 1513/3712 - Ausgabedatum: 18.06.2011 * * 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/

**Follow-Ups**:**Re: st: Merge Panel Datasets***From:*Phil Schumm <pschumm@uchicago.edu>

**References**:**st: Merge Panel Datasets***From:*"Diana Beketova" <diana.beketova@gmx.de>

**Re: st: Merge Panel Datasets***From:*Phil Schumm <pschumm@uchicago.edu>

**AW: st: Merge Panel Datasets***From:*"Diana Beketova" <diana.beketova@gmx.de>

**Re: AW: st: Merge Panel Datasets***From:*Phil Schumm <pschumm@uchicago.edu>

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