S . ▁cities , ▁at ▁ 1 5 . 4 %. ▁San ▁Francisco ▁also ▁has ▁the ▁highest ▁percentage ▁of ▁same - sex ▁households ▁of ▁any ▁American ▁county , ▁with ▁the ▁Bay ▁Area ▁having ▁a ▁higher ▁concentration ▁than ▁any ▁other ▁metropol itan ▁area . ▁ ▁San ▁Francisco ▁ranks ▁third ▁of ▁American ▁cities ▁in ▁median ▁household ▁income ▁with ▁a ▁ 2 0 0 7 ▁value ▁of ▁$ 6 5 , 5 1 9 . ▁Med ian ▁family ▁income ▁is ▁$ 8 1 , 1 3 6 , ▁and ▁San ▁Francisco ▁ranks ▁ 8 th ▁of ▁major ▁cities ▁world wide ▁in ▁the ▁number ▁of ▁billion aires ▁known ▁to ▁be ▁living ▁within ▁city ▁limits . ▁Following ▁a ▁national ▁tr end , ▁an ▁em igration ▁of ▁middle - class ▁families ▁is ▁contrib uting ▁to ▁w iden ing ▁income ▁dispar ity ▁and ▁has ▁left ▁the ▁city ▁with ▁a ▁lower ▁proportion ▁of ▁children , ▁ 1 4 . 5 %, ▁than ▁any ▁other ▁large ▁American ▁city . ▁ ▁The ▁city ' s ▁pover ty ▁rate ▁is ▁ 1 1 . 8 % ▁and ▁the ▁number ▁of ▁families ▁in ▁pover ty ▁stands ▁at ▁ 7 . 4 %, ▁both ▁lower ▁than ▁the ▁national ▁average . ▁The ▁un emp loyment ▁rate ▁stands ▁at ▁ 4 . 8 % ▁in ▁the ▁greater ▁San ▁Francisco ▁Bay ▁Area ▁. ▁ ▁Hom eless ness ▁ ▁Hom eless ness ▁has ▁been ▁a ▁chron ic ▁and ▁controvers ial ▁problem ▁for ▁San ▁Francisco ▁since ▁the ▁early ▁ 1 9 7 0 s ▁when ▁many ▁ment ally ▁ill ▁patients ▁were