Today's 'Fun with Numbers': More on graduation rates

So, the rule-of-thumb is that about 1/4 of American adults are college graduates; and something like 20% are high-school dropouts. But the post-war boom in education has really transformed the attainments of the citizenry. (Case in point: the Iowa- class BBs were designed to be operated by sailors who possessed a third-grade education. The 1980s refit raised that a bit.)

Which leads us to some interesting boring questions:

1) What year did a majority of American adults have a HS education?

from the Stat Abstract, the ready-to-hand 2004-5 edition:
1960: 41.1% HS 7.7% college grad or more
1970: 52.3% HS 10.7% (note that Linda was part of the elite: the most educated 10%)

linear interpolate: add per yr: 1.12% and +0.3%;
which gives us a rough'n'ready answer of: About 1968.

Which might be an interesting coincidence: "1968" being, after all, The Year It Changed.

Ok, I'm interested enough in the answer to actually look it up in the 1970 Stat Ab:
1965: 49.0%
1966 na
1967 51.6%
1968 52.6%


The more robust, closer to 'real' answer: probably about 1966.

From this, we learn that the day I started college, I became part of the better-schooled half of the populace? Wow.

Further: today's citizenry is twice as educated as 1961??
(2003: 84.6% of adults have a HS diploma, vs. 1960: 41.1%)

A question for another day is the depreciation of the HS diploma:
my mother-in-law's Boston Latin dipoma from about 1940 probably certified more actual 'education' than most college degrees do today.

A second interesting boring question emerges:
2) In what year did the percentage of college grads exceed the number of HS
dropouts? (bringing the nominal average up past "HS diploma" level. Yes, yes, there's data on Associates degrees, and post-grad education tips the balance, too.
I could go look up DoE data on "average years completed", too. But this stat I'm thinking of is slightly different from the simple 'average'.)

College grads dropouts
1990 21.3% 22.4%
1995 23.0% 18.3%

linearly interpolating, we get
1991 = ~21.64% ~21.58%

Which is slightly interesting: the landscape changed the very year I started having kids.