Some general process measures have a stronger evidence base than others. Those based on guidelines have the strongest evidence base; those derived from basic first principles supported by some research findings are relatively weaker, but are often sufficient for the task at hand. A consistent source of tension is the distinction between the clinically derived fine-tuning of the definition of a quality measure and the limitations of available data sources (which often do not contain sufficient information to act on such distinctions). Although some excellent technical measures were found, the overall development of technical measures seems less advanced than that of the general process measures.