gen widowhood08_11 = yearin_11 - f41a11_11 if 2011>=f41a11_11>=2008
replace widowhood08_11 = yearin_11 - f41a11_14 if 2011>= f41a11_14 >=2008
生成的新变量全是缺失值
gen widowhood08_11 = yearin_11 - f41a11_11 if 2011>=f41a11_11>=2008
replace widowhood08_11 = yearin_11 - f41a11_14 if 2011>= f41a11_14 >=2008
生成的新变量全是缺失值