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From |
"Hofbaur, Ulrich" <Ulrich.Hofbaur@whu.edu> |

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

Subject |
st: Different results for 1:1-merging using the same variables (int & string) |

Date |
Wed, 13 Feb 2013 18:07:12 +0000 |

Dear all, I have an issue with conducting a 1:1-merge in Stata. The merge is based on two variables. The 1. variable (string) consists of exactly 6 digits. The 2. variable (integer) consists of exactly 4 digits (no variation in the length of digits in either of the two variables). I tried two versions, and the they both yielded different results. Please, further note that I use the same file to merge and the variables differ Option 1: Defining a 10-digit string variable. Therefore, convert "var 2" to string and then sum var1 and var2. Hence, I obtain" var3" (which is a 10-digit string; again no variation w.r.t to the length of 10-digits) and merge (1:1) on "var3". → Results in 15,839 matches Option 2: Merge (1:1) on var1 and var2 as separate variables → Results in 14,227 Does anybody know where this difference comes from. My gut feeling tells me that Option 2 is the more reliable one. However, I lack evidence on that. The abbreviated Do-File is attached. Thank you very much for your support! Best, Ulrich ******* Do File ************** use F:\001_Forschung\Daten\Cash&Acquisitions\file_A_prelim.dta, clear * Option 1 gen acquirorcusip_year=cusip_6dgt+next_year //corresponds to var 3 in the above description gen length_cusip_6dgt=length(cusip_6dgt) gen length_announcement_year=length(next_year) gen length_acquirorcusip_year=length(acquirorcusip_year) sum length_cusip_6dgt length_announcement_year length_acquirorcusip_year Variable Obs Mean Std. Dev. Min Max length_cus~t 196217 6 0 6 6 length_ann~r 196217 4 0 4 4 length_acq~r 196217 10 0 10 10 * Option 2 gen announcement_year=next_year // corresponds to var 2 in the above description. Rename due to file_B destring announcement_year, replace gen acquirorcusip=cusip_6dgt // corresponds to var 1 in the above description. sort acquirorcusip announcement_year save file_A.dta, replace * Option 1: Merge on the joint string variable use file_A.dta, clear merge 1:1 acquirorcusip_year using F:\001_Forschung\Daten\Cash&Acquisitions\file_B.dta Result # of obs. ----------------------------------------- not matched 191,640 from master 180,378 (_merge==1) from using 11,262 (_merge==2) matched 15,839 (_merge==3) ----------------------------------------- * Option 2: Merge on two separate variables use file_A.dta, clear merge 1:1 acquirorcusip announcement_year using F:\001_Forschung\Daten\Cash&Acquisitions\file_B.dta Result # of obs. ----------------------------------------- not matched 194,864 from master 181,990 (_merge==1) from using 12,874 (_merge==2) matched 14,227 (_merge==3) ----------------------------------------- * * 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/

**Follow-Ups**:**Re: st: Different results for 1:1-merging using the same variables (int & string)***From:*Jeph Herrin <stata@spandrel.net>

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