An interesting study would be to take the population of unvaccinated and count how many are that way due to antivax ideology and how many due to some other cause.

Furthermore, it'd be interesting to examine the measles cases and see what population they come from.

I see an article castigate the antivaxxers and then say most measles occur among unvaccinated populations. Is the article saying the two populations are the same? No solid link is offered, yet the two groups are mentioned together leading a non-careful reader to conclude the antivaxxers are to blame.