Sorry, I was bored ploughing through this thread and I noticed this interesting comment. I haven't studied the matter in depth but I'd have thought about the same percentage of teams would do as well is the second half of the season. Do you have any figures to prove this?
Well I was bored, and this was easy to run, so I checked the numbers for League One last season.
Teams earned a total of 765 points in their first 23 games and 744 in their final 23 games. All well and good so far.
11 teams gained more points in the first half of the season than the second half, getting worse as the season goes on. The range runs from Bradford (1 point difference) to Walsall (15).
11 teams gained less points in the first half of the season than the second half, improving as the season went on. Bookends were Charlton (2 points) to Wimbledon and Bristol Rovers (14).
Luton and Rochdale both gained the same number of points in each half.
So a pretty even split, which makes sense in football because any time a team loses an extra game, someone else should be winning one.
One thing that is definitely noticeable is that teams at the top end after 23 games tended to do worse, and teams at the bottom tended to improve. Of the 12 highest teams after 23 games, 3 improved their performance, 1 stayed the same, and 8 declined. For the 12 lowest teams after 23 games the exact opposite is therefore true - 3 got worse, 1 stayed the same, 8 improved.
Therefore, using one tiny sample as evidence, we can't support the idea that teams generally struggle to maintain their points performance. But we can say that Oxford, in the play off spaces after 23 games this year, are prime candidates to dip.
A quick edit to comment on the play off places. Doncaster (-5), Sunderland (-9) and Pompey (-14) all made the play offs despite a second half decline, whilst Peterborough (-10) just missed out and finished 7th. More ominously, the three teams missing are Luton (0), Charlton (+2) and Barnsley (+7). You might remember that they are the three that got promoted...