When different studies use the
same angular velocity for measurement, these can be compared to one another, so long as differences between the populations tested are acknowledged, and so long as the
dynamometer used is the
same in both cases, as differences have been observed between brands (Francis & Hoobler, 1987; Thompson et al. 1989; Gross et al. 1991).
The trouble is that drivers don't always see the
same efficiency in real - world driving that the EPA testers manage, so Mazda set all of its consumption targets according to driving habits of actual customers who don't drive on a
dynamometer in a lab.