各位stata大神,小弟目前在做SEOs eventstudy, 现在遇见了一个很白痴的问题,哭求帮助
小弟想对每一家公司(样本1080家)都用announment year年度的financial leverage减去announcement 前一年的financial leverage, 请问如何操作
company_id date announcement year year financial leverage
2 2006.12.28 2007 2006 1.041263
2 2006.12.29 2007 2006 1.041263
2 2006.12.30 2007 2006 1.041263
2 2007.1.4 2007 2007 1.047045
2 2007.1.5 2007 2007 1.047045
2 2007.1.6 2007 2007 1.047045
2 2007.1.7 2007 2007 1.047045
3 2001.12.27 2002 2001 0.941398
3 2001.12.28 2002 2001 0.941398
3 2001.12.29 2002 2001 0.941398
3 2001.12.30 2002 2001 0.941398
3 2002.1.5 2002 2002 0.943815
3 2002.1.6 2002 2002 0.943815
3 2002.1.6 2002 2002 0.943815
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