Good point. And I don't know how the vocabulary test was made. I think the monotonicity can be explained by, in general, people who read marginally more are mar

Good point. And I don't know how the vocabulary test was made. I think the monotonicity can be explained by, in general, people who read marginally more are marginally exposed to more things (even after to discounting for the important fact that there is less free time and they're more intellectual, etc.). But it's a very good point. It seems like there are a lot of different factors.