The percentage of 5-4 decisions being handed down is practically meaningless without relating it to how controversial or "hard" the questions being decided are.

The percentage of 5-4 decisions being handed down is practically meaningless without relating it to how controversial or "hard" the questions being decided are. That of course, is fundamentally hard to quantify, although you may make some headway by dividing up decisions based on whether there were circuit splits, how (in)consistent the decisions of lower courts that evaluated the case were, the splits for the lower courts, etc. Moreover, cases often address multiple questions and a 5-4 decision can be handed down even when many or most of the questions answered were subject unanimous or nearly unanimous agreement. By the same token, a unanimous or near-unanimous decision could have been reached in spite of radically diverging rationales from the various justices.