Database: scholar_minus_1_0
Question: what keyphrase does Brian DeRenzi write about that gets most citations ?
SQL: select distinct t1.keyphrasename , sum ( t2.numcitedby ) from paperkeyphrase_keyphrase as t1 join paper as t2 on t1.paperid = t2.paperid join writes as t3 on t2.paperid = t3.paperid join author as t4 on t3.authorid = t4.authorid where t4.authorname = 'brian derenzi' group by t1.keyphrasename order by sum ( t2.numcitedby ) desc ;