I don't have stats to back this up, but anyone tha watches a lot of NBA games will likely agree.........
Third quarters of NBA games are traditionaly the lowest scoring of the quarters. Also, the first part of the 4th quarter tends to be a bit slower paced, as the team in the lead begins working the clock.
When defenses press, it also usually starts in either the 3rd of 4th quarter.
The opposite point of view about the halves totals is that you do get a lot of intentional fouls late in he game, which can push a total OVER. This happens in games where one team is down by 4-8 points. If you think the game wil b very close, intentionlly fouls may not be a factor. Blowouts also tend to be lower scoring in te 2H.
I think it's very important to try and speculate -- WHAT IS THE SCORE LIKELY TO BE WITH TWO MINUTES REMIANING? If you can correctly predict those games that are blowouts/tight games, versus games where the margin is 4 to 8 points, then that's half the battle right there.
FWIW, I have no ability to predict 1H totals, but have done reasonably well in 2Hs by looking at shootin percentages, rebounding, and the general flow of the game -- where it's often wise to go the OPPOSITE in he 2H.
Good luck,
Nolan Dalla