That doesn't show how good a state does graduating students from high school, but rather how good wherever they were living when they were 16 to 18. If someone is 70, they were in HS at a time when about 65% of students graduated, and only 40% of the adult population over 25 was a HS graduate. For someone who is 55 or younger, they were in HS at a time when 86-88% of students graduated (a rate that has now held for close to 40 years).
A state that has a relatively low component of older persons (such as those in the West that have had high growth, will have a larger percentage of adults who have completed high school. But this is just another way of saying that they have a relatively large share of adults under 55. States that have seen large scale emigration may have low levels of adult completion. People move more in their 20s and 30s. If a HS graduate leaves the state, then the relative share of older adults increases, and the overall HS completion rate decreases.
I don't think you understood what my point was. When I said "[t]hat doesn't show ..." I was referring to what the census report shows. It does not necessarily show how the HS in a state are doing since it reports on the percentage of adults older than 25 who lived in the state who had graduated from HS. An adult who is 70 would have graduated (or not) over 50 years ago. If he happened to live in the same state, then it shows how good the education system (at least in terms of keeping students in school until they are in 12th grade) was 50 years ago. If the adult has moved since HS, then it measures how good the education system was at that time.
At best, it might show how good a state is at attracting HS graduates, or at retaining them after graduation. The attractor is usually the availablity of jobs. NH attracts college graduates (almost all who are also HS graduates) who work in high tech firms in Massachusetts but who want to live where there are lower taxes.
I wasn't commenting on how HS graduates vote at all.
Of course not. But my explanation about emigration may do so. RI had modest growth up until about 1970. It has been stagnant since then, increasing only by about 10% over 30 years. This population stagnation began just about the time the baby boomers got out of HS/college and began their work career. If the population isn't growing, it means that there are not jobs. So the baby boomers, who will be more likely to have a HS degree than their parents, are going to move to Boston or New York or beyond in search of a job. Someone who is 40 YO, with kids in school and a house are less likely to pull up stakes. Among the young, there may even be differentiation on the basis of education, with those without a HS degree sticking around, working in lower-skilled jobs.
30 years later now, the relative share of the population that is around 50 is somewhat less than other states, while the relative share of the population that is in its 60s and 70s, is greater. And this older population is less likely to have a HS degree (those who are 50 are just as likely as those who are 20).
An interesting chart in the census report is the one that shows the percentage of the adult population with a HS degree vs. the percentage of the population between 25 and 29 who have a HS degree. For 40+ years the rate for 25-29 YO has stayed about the same, but the rate for the adult population has steadily increased, as the new adults replace the old adults as they die. The increase in the rate for the US adult population is high enough that the current rate for Texas is about the national rate in the early 90s.
I wasn't arguing that it was
