As you just read, we installed the ridge vent on this home in 1990 and found it to be absolutely worthless.  Puffing smoke up under the vent in a hot, stifling attic showed NO movement of air up through the vent.  So we went back and added the six dormer vents.  The attic was still too hot so we blocked off all the dormer vents, installed a 16" German fan in the center, blocked off the oversized gable vents and now drawing cool air in through the soffits.  Over 20 years of testing and we finally get it right?  I once thought that passive vents would be suffice when using a radiant barrier which makes attics hotter.  On this home the passive venting was many times what the minimum USB code required and was still not enough.  With summer soon upon us, we will be doing more attic temperature testing but one thing is certain:  after having experimented with every type of vent combination available it appears the best way to remove hot, stagnant air is by using  a reliable powered ventilator.