Credit report - joining the electorol roll?

I recently got refused credit for a catalog and was quite shocked as i hadn't been refused credit before, i automatically umed i had an awful credit report, but just checked it on experian.com and i have a score of 870 ("Fair" - 10 more points needed for "Good") it says i should join the electoral roll to boost my score...does anybody know how much difference this makes? I check my account and dates obsessively, so no bills/payments are ever late.