Hi there,

I'm trying to first difference my variable on industrial production, but all I get are missing values. What am I doing wrong?

clear
input int DATE double INDPRO
6940 53.2837
6971 53.5675
6999 53.7364
7030 53.1571
7060 53.5566
7091 53.5534
7121 53.4808
7152 53.1195
7183 53.1786
7213 53.4617
7244 53.409
7274 53.4536
7305 53.7071
7336 53.7262
7365 53.5481

tset DATE, monthly
gen IP = L.INDPRO

Why is this yielding noting but missing values?