The question of the optimal spread between bank lending rates and rates that banks pay on deposits, which is fair to bankers, depositors and borrowers, has dogged economies for some time. In Ghana, there is widespread perception that the spread is too wide. Bankers, on the other hand justify the spread on the basis of economic variables that affect them. This paper contributes to the literature by identifying, in the case of Ghana, the short-run response of the net interest margin of banks to changes in bankspecific, industry-specific and macroeconomic variables within the broad framework of Ho and Saunders (1981). We find that increases in the following factors significantly increase net interest margin -bank market power (or concentration), bank size, staff costs, administrative costs, extent of bank risk aversion and the rate of inflation. On the other hand, increases in the following variables decrease net interest margin significantly -bank excess cash reserves, the central bank lending rate, management efficiency and the passage of time. To help reduce interest rate margins, we recommend that banks should not get too big, the central bank should consider lowering the capital adequacy ratio and banks should be required to pass on to borrowers the full extent of reductions or increases in the central bank lending rate.

A competitive banking system helps lower transaction costs and risks. It also helps make financial markets more efficient. In Ghana however, observers believe that the banking industry is not competitive and point to the huge spread between bank lending and borrowing rates as evidence. The Ghanaian banking industry is analysed for evidence of market power by computing the Lerner Index of banks using quarterly data from 2001 to 2006. The evidence is that Ghanaian banks possess market power. Factors that significantly explain the market power of Ghanaian banks are: bank size, efficiency of banks with respect to staff costs, the macroeconomic environment and time.

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