Both the NII and NI are important but for different reasons.  Changing interest rates directly affect interest income and dividend and interest expense.  The difference between these two is the NII so in a changing rate environment, actual or simulated, the NII will change depending only on market conditions and the repricing attributes of the balance sheet components.  The NII is not influenced by operating expenses, fee income, or the loan loss provision.  As such, it is the most important barometer of interest rate risk.  The NI on the other hand, is important because it is affected by the changes in the NII and it is, literally, the bottom line.  However, the NI is also affected by operating expenses, fee income and the loan loss provision.  Thus, if loan losses and/or operating expenses are too high or fee income too low such that the ROA is low, even a small change in interest rates and thus the NII could cause a dramatic percentage decline in the NI.  This may be incorrectly interpreted as an interest rate risk problem when it is an income problem due to high expenses, high loan losses, or insufficient fee income, all of which are unrelated to interest rates, at least in the short run.