df = readtable("E:/McNair/Projects/LBO/Clean/STATApredictLBOclean.txt", separator = '\t');
===Specify which observations are valid for matching.===
*For now, we filter out all firms that were never granted a single patent in the period 1970-2015
*For firms that LBO, we also drop their observations in all other years from the list of candidates to match to other LBOs