FootyMaths
alerted me this week to a new
thread on Reddit which collates the various AFL Power Rankings there
are around the net. It includes my rankings, along with those of FootyMaths,
Matter of Stats, Fox Sports, The Roar, Sportsfan, Footy Prophet, Squiggle,
ASAP, and /u/ Statisticc. (I won’t include all the hyperlinks here – you can click
on the Reddit page and follow through to the individual ranking systems from
there.)
The comments were
relatively fair, in that there weren’t too many of the ‘these rankings are
stupid, so-and-so obviously knows nothing about football’ variety. One thing
that I did note though was that there seemed to be a general feeling among
commenters that early-season results, such as Geelong beating Hawthorn, should
have a higher weight.
Is this the right view to
take? I’ve dealt with this topic before as early season results seem to make a
lie of my and other rankings. There are reasons to think that clubs do change
more in ability between seasons than within seasons. Players get half a year
older, their abilities have more time to improve or deteriorate, and there are
important changes in playing lists. You wouldn’t dream of, for example, having
a National Basketball Association rankings system that did not account for
events like LeBron James moving back to Cleveland.
It occurred to me that I could
test this by comparing how much my rankings changed at the start of the season
with the middle of the season. I didn’t compare this against the end of the
season in case some clubs partially throw in the towel once their finals hopes
are gone. If a new year does bring big changes, then my thinking is that my rankings
should have larger changes at the start of the season as they scurry to adapt
to the new season’s order. More specifically I looked at the changes in ranking
points across clubs from Rounds 1-6 for each year (from 2011) compared with changes
from Rounds 8-14 (because of byes, these seven rounds typically cover only six
matches for each club).
Are there bigger changes at
the start of the season? Not really (this actually surprised me a little). I
won’t put all my results here – the more mathematically-minded among you can probably
go back and basically verify this for yourselves if you want – but
the variation in changes don’t appear to be any larger on average at season’s
start. Maybe this changes if you look at a longer period than five years, but
at least it’s not clear to me yet that I should be attaching any special
significance to the first few rounds’ results.
Big changes happen within
seasons too. For example, last season Fremantle fell away in the second half of
the season. If a new season had started in say, July, then perhaps more may
have been made of the Dockers’ drop, instead of this only being focussed on now
the new season has started. Fremantle’s fall really started in mid-2015, but
fewer people noticed because it was the middle of the season and they were
still sitting on top of the 2015 ladder. Another example, in the opposite direction,
is Sydney picking up steam in the middle of 2014.
There is another way of
looking at this question though, which may be more pleasing to those who hold
that you should attach a lower weight to last season’s results. That is, I did
find some evidence that there is a stronger relationship between changes in rankings
points at different points within the same season than between seasons. For
example, West Coast and the Bulldogs started well in 2015, and their ranking
points kept on improving throughout the season as it became clearer and clearer
that they were big improvers last year.
Anyway, getting back to the
rankings themselves, this week the big developments are Adelaide moving into
the top four after thrashing Port, and Carlton returning to the bottom after
getting thrashed by Sydney – Essendon actually winning a match also had
something to do with that. The big improver two rounds in is the Gold Coast
Suns, who have picked up ten ranking points so far, while Fremantle have lost
around the same number of points. Not that you should be placing too much
weight on these early season results. (Or should you … ?)
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