Given my composer/work database (needed to keep my collection in some kind of order, and so I don't buy something I already have...), I was curious as to the dating of symphonies labeled in keys vs. those without, and the nature of the transition from primarily tonal works to primarily atonal works. Obviously a coarse approach, because key labels or absences don't necessarily reflect attitudes toward tonality. And there's infinite variation between completely tonal and completely atonal, as we all know. So, with those caveats aside:
With 614 composers and 3688 symphonies, I spent an hour or so totaling them up in 5 year intervals from composers born from 1700 to 1938.
seems like 4 main periods:
born between 1700-1854, 202 composers: were generally all tonal
born between 1855-1879, 156 composers: 80-97% tonal, 5-13% atonal, and 3-10% both
born between 1880-1889, 67 composers, 65% tonal, 20% atonal, 15% both
born between 1890-1914, 143 composers, 32% tonal, 43% atonal, 26% both
born between 1915-1934, 43 composers, 10% tonal, 60% atonal, 35% both
what struck me was:
-how many folks were writing symphonies emphasizing keys (tonality) into the later 20th century.
-The high number of tonal composers who later shifted (peer pressure, audience expectations?) to atonality (almost 20% from 1855-1934). These folks generally shifted in 1940s-1950s.
-many folks writing "atonal" symphonies actually had tonal first symphonies: Ives, Schreker, Stravinsky, Yamada, Gal, Nepomuk David, Holler, Bunin, Nasidze, etc.
-many (generally atonal) composers would write symphonies labeled in keys interspersed with their atonal works (neoclassical influences?)
-the latest purely tonal symphonists were typically soviets (the realist school forced by soviet thought, emphasizing lyricism and connection with the masses?): Kabalevsky, Popov, Shostakovich, Golubev, Khrennikov, Yurovsky, Svetlanov, Adriasov, etc.
-symphonies seem to have become less important in ouevres (totals decline every 5 years since 1950).
In terms of when the symphonies were first published/heard?:
1700-1889 (n=1845) - 100% tonal, 0% atonal
1889-1919 (n=424) - 97% tonal, 3% atonal (n=9 atonal symphonies)
1920-1949 (n=741) - 56-65% tonal, 44-35% atonal (n=294 atonal symphonies)
1950-1989 (n=642) - 29-42% tonal, 71-58% atonal (n=199 tonal symphonies)
1990-2009 (n=36) - 100% atonal
Anyway, food for thought.