How to calculate Buy-and-hold Abnormal Return (BHAR) ？

[xipei li]

We use the income from May of T+1 to April of T+2 as T annual income.BHAR is equal to the multiplier of each company's 12-month revenue in a year, and then subtracts the 12-month revenue multiplication of the market in a year.For example, A company's 2015 BHAR is equal to the company's monthly yield from May 2016 to April 2017, and then subtracted the yield from May 2016 to April 2017.This is too complicated, I really can't figure it out, so ask questions.
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* Example generated by -dataex-. To install: ssc install dataex
clear
input str6 code str7 date double(IT MT)
"000002" "2009-01"  .091473  .157394
"000002" "2009-02"  .015625   .08893
"000002" "2009-03"  .158042  .223024
"000002" "2009-04"  .024155  .076364
"000002" "2009-05"  .148585  .071731
"000002" "2009-06"  .314909  .088737
"000002" "2009-07"  .047843  .148047
"000002" "2009-08" -.296407  -.15897
"000002" "2009-09"  .108511  .045235
"000002" "2009-10"  .104607  .120721
"000002" "2009-11"  .001738  .146828
"000002" "2009-12" -.062446  .025708
"000002" "2010-01" -.135985 -.032345
"000002" "2010-02"  .009636  .066523
"000002" "2010-03"  .007423  .042699
"000002" "2010-04" -.178947 -.070492
"000002" "2010-05" -.066826 -.085053
"000002" "2010-06" -.059639 -.092684
"000002" "2010-07"  .222714  .152968
"000002" "2010-08"  .015682  .091707
"000002" "2010-09" -.002375  .014685
"000002" "2010-10"  .154762  .092551
"000002" "2010-11" -.161856  .008053
"000002" "2010-12"   .01107   -.0194
"000002" "2011-01" -.002433 -.049277
"000002" "2011-02" -.004878  .097416
"000002" "2011-03"  .064951 -.005443
"000002" "2011-04" -.024166 -.029671
"000002" "2011-05" -.063769 -.073427
"000002" "2011-06"  .077806  .037579
"000002" "2011-07" -.035503  .021129
"000002" "2011-08"        0 -.028933
"000002" "2011-09" -.111656 -.117144
"000002" "2011-10"  .104972   .03965
"000002" "2011-11"   -.1175 -.044145
"000002" "2011-12"  .058074 -.155997
"000002" "2012-01"  .024096  .007288
"000002" "2012-02"  .082353  .130467
"000002" "2012-03"        0 -.072395
"000002" "2012-04"  .084541  .075331
"000002" "2012-05"  .030067  .020294
"000002" "2012-06" -.036757 -.064925
"000002" "2012-07"   .05041 -.092077
"000002" "2012-08" -.131094  .019197
"000002" "2012-09"  .051122   .01457
"000002" "2012-10" -.013049   .00558
"000002" "2012-11"  .051683 -.108443
"000002" "2012-12"  .156571  .166233
"000002" "2013-01"  .186759  .065083
"000002" "2013-02" -.000833  .043567
"000002" "2013-03" -.103333 -.033948
"000002" "2013-04"  .025093 -.032165
"000002" "2013-05"  .102837   .13469
"000002" "2013-06" -.177796 -.163374
"000002" "2013-07" -.033503  .062773
"000002" "2013-08" -.006303  .092286
"000002" "2013-09" -.034884  .048109
"000002" "2013-10"  .008762 -.020632
"000002" "2013-11"  -.04886  .071771
"000002" "2013-12" -.083333  -.03295
"000002" "2014-01" -.080946  .005079
"000002" "2014-02" -.089431  .043985
"000002" "2014-03"  .203869 -.017824
"000002" "2014-04" -.023486 -.012822
"000002" "2014-05"  .142649  .024008
"000002" "2014-06" -.032749  .040563
"000002" "2014-07"  .197098  .092952
"000002" "2014-08" -.078788  .060615
"000002" "2014-09"  .006579  .143076
"000002" "2014-10"  .023965  .023014
"000002" "2014-11"  .159574  .063455
"000002" "2014-12"  .275229 -.010609
"000002" "2015-01" -.056115  .072194
"000002" "2015-02" -.028201   .07249
"000002" "2015-03"  .083922  .224049
"000002" "2015-04"   .05644  .189475
"000002" "2015-05" -.017123  .270192
"000002" "2015-06"  .011847 -.076295
"000002" "2015-07"  .010236 -.166447
"000002" "2015-08" -.026798 -.131148
"000002" "2015-09" -.077536  -.05459
"000002" "2015-10"  .073841  .218789
"000002" "2015-11"  .102414  .108848
"000002" "2015-12"  .621102  .076944
"000002" "2016-07" -.268932  .010287
"000002" "2016-08"  .454492  .053706
"000002" "2016-09"  .049739 -.003338
"000002" "2016-10" -.047765   .04209
"000002" "2016-11"  .082665  .037181
"000002" "2016-12" -.238325 -.034747
"000002" "2017-01"  .006326 -.017722
"000002" "2017-02" -.007253  .052976
"000002" "2017-03"  .002435 -.015306
"000002" "2017-04" -.052478 -.056799
"000002" "2017-05"  .090256 -.076485
"000002" "2017-06"  .174506  .041879
"000002" "2017-07" -.064077  .003885
"000002" "2017-08"  .027624  .038274
"000002" "2017-09"  .130004  .010294
"000002" "2017-10"  .103238 -.010664
end

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Listed 100 out of 249277 observations

[Jiao Jian]

firstly, you need to generate some vars, like generate a sequent id variable, -by code egen id=_n. - and a year variable ,a month variable. then use -forvalues i=1/_N{ }- to calculate this value, should be convenient.