Since the BOP have negative values, log form cannot be applied,
while
the SDRs can take the log form. So a log-linear model can be
applied.
First generate a log series of SDRs by typing "genr lnsdr = log sdr"
in the command line. And then regress lnsdr on bop by using the
"Estimate Equation" from the "Quick" option. Typing "lnsdr c
bop"
in the dialog box, and here are the results:

No, BOP has negative vaules. Natural logarithms for negative values
do not exist.