Pengaruh perubahan suku bunga terhadap perubahan Net Interest Margin (NIM) ; studi kasus 16 bank umum konvensional yang tercatat di BEI periode 2005-2009 = The effects of changes in interest rates to changes in bank's Net Interest Margin (NIM) : case study 16 conventional commercial bank listed on Indonesia Stock Exchange in period of 2005-2009