bysort number:reg hpi trend
predict hpi1
bysort number:egen average_hpi = mean(hpi)
bysort number:egen TSS=sum((hpi-average_hpi)^2)
bysort number:egen RSS=sum((hpi-hpi1)^2)
bysort number:egen ESS=sum((hpi1-average_hpi)^2)
bysort number:gen R方=1-(RSS/TSS)