# Dupont analysis of banks

I've been analyzing banks balance sheet. However, I am getting confused regarding definition of ratios. For instance, some authors state

Net Profit Margin = (Net profit)/Net interest income others as Net Profit Margin = (Net profit)/total income i.e. some of interest income and other income.

Similarly, some authors define ROA= Net profit/Total assets while others define it as ROA= Net profit/Average Total assets

Is there any comprehensive source/reference for ratio analysis of banks?