It seems that its a litle like saying 'declining health correlates with death', yet your still stuck at trying to predict declining health(or the NPA trend in the case of banks)
The only thing that predicts bank failures is irresponsible lending. You don't need to be an economist to spot this: When you see many of your irresponsible, lazy, spender friends get hefty credits with no job or income stability; you can be sure it's only a matter of time before many banks get bankrupt.