But g,, and g,, can both be measured, and it is well established that for no value of p that is close to observed capital shares is it the case that F is even approximately uniform across countries. Here 'Denison's Law' works against us: the insensitivity of growth rates to variations in the model's underlying parameters, as reviewed earlier, makes it hard to use the theory to account for large variations across countries or across time. To conclude that even large changes in 'thriftiness' would not induce large changes in U.S. growth rates is really the same as concluding that differences in Japanese and U.S. thriftiness cannot account for much of the difference in these two economies' growth rates. By assigning so great a role to 'technology' as a source of growth, the theory is obliged to assign correspondingly minor roles to everything else, and so has very little ability to account for the wide diversity in growth rates that we observe.