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The Premier League has thrown up numerous surprises this season

It is the Premier League season that has everyone scratching their heads.

Champions Chelsea are down in 14th. Leicester, bottom at Christmas last year, are top less than 12 months later.

In fact, as this image below shows, the old cliche that anyone can beat anyone has never been more apt. Undoubtedly, there have been some strange results.

But just how unusual has this season really been and what have been the key factors in making it so unpredictable? BBC Sport crunches the numbers to find out.

Chelsea go from champions to chumps

Chelsea's start to the season is the worst of any reigning Premier League champion.

In fact, Blackburn are the only other side to have picked up fewer than 20 points in the first 15 games of a title defence.

Chelsea and Manchester United have mounted the best starts to a defence, both registering 40 points in 2005-06 and 1993-94 respectively.

Points by defending champions in first 15 games Season Team Points Season Team Points 2005-06 Chelsea 40 1993-94 Man Utd 40 2000-01 Man Utd 36 2011-12 Man Utd 36 2006-07 Chelsea 35 1994-95 Man Utd 34 2009-10 Man Utd 34 2003-04 Man Utd 34 2014-15 Man City 33 2012-13 Man City 33 2007-08 Man Utd 33 1999-00 Man Utd 33 2002-03 Arsenal 32 2004-05 Arsenal 31 1997-98 Man Utd 31 2008-09 Man Utd 31 2010-11 Chelsea 29 1996-97 Man Utd 26 1998-99 Arsenal 25 2013-14 Man Utd 22 2001-02 Man Utd 21 1995-96 Blackburn 18 2015-16 Chelsea 15

Tight at the top

This is reasonably unusual. There are just six points between top side Leicester and fifth-placed Tottenham - it's only been that close one other time in the past 10 seasons.

Big boys get beaten

Last season's top two of Chelsea and Manchester City have lost a combined total of 12 games this term - the highest over the past 10 seasons.

Defeats in first 15 games for previous season's top two Season First Second Total 2015-16 Chelsea (8) Man City (4) 12 2014-15 Man City (2) Liverpool (6) 8 2013-14 Man Utd (5) Man City (4) 9 2012-13 Man City (0) Man Utd (3) 3 2011-12 Man Utd (1) Chelsea (4) 5 2010-11 Chelsea (4) Man Utd (0) 4 2009-10 Man Ud (3) Liverpool (5) 8 2008-09 Man Utd (2) Chelsea (2) 4 2007-08 Man Utd (2) Chelsea (2) 4 2006-07 Chelsea (2) Man Utd (1) 3

Away the lads

Teams are loving an away day this season.

There have been 51 away victories from 150 Premier League games this term - that's 34% of fixtures.

Of the 9,130 games in Premier League history, 27.25% have ended with a win for the visitors.

New boys bucking the trend?

The three promoted teams of Bournemouth, Watford and Norwich are all currently out of the relegation zone, which you might think is unusual.

Lately, it's not been that uncommon.

In fact, it has happened twice in the previous five seasons. Newcastle United, West Brom and Blackpool were above the drop zone at this point in 2010-11, as were QPR, Norwich and Swansea in 2011-12.

However, those are the only three times the feat has occurred in the past decade, and rarely do one of those sides beat the champions, as Bournemouth did when winning 1-0 at Chelsea on Saturday.

Match of the Day presenter Gary Lineker is enjoying his former club Leicester being top of the table

Will Leicester win the league?

The team that's top in early December is most likely to go on to claim the title, right?

If history is any indicator, Leicester City have actually got almost a 50-50 chance of causing a massive shock and becoming champions.

Where does the team top after 15 games finish? Season Team Final position Season Team Final position 1993 Norwich 3rd 2005 Chelsea 1st 1994 Man Utd 1st 2006 Chelsea 1st 1995 Man Utd 2nd 2007 Man Utd 1st 1996 Newcastle 2nd 2008 Arsenal 3rd 1997 Arsenal 3rd 2009 Liverpool 2nd 1998 Man Utd 2nd 2010 Chelsea 1st 1999 Aston Villa 6th 2011 Man Utd 1st 2000 Man Utd 1st 2012 Man City 1st 2001 Man Utd 1st 2013 Man Utd 1st 2002 Liverpool 2nd 2014 Arsenal 3rd 2003 Arsenal 2nd 2015 Chelsea 1st 2004 Chelsea 2nd 2016 Leicester ?

In Premier League history, the team top after 15 games has gone on to win the title 47.8% of the time. And that rises to 72.7% over the past 11 seasons.

Manchester United have been top after 15 games eight times - and have converted that into a title on six occasions

But of the eight different clubs to be top at this stage, only three - Manchester United, Manchester City and Chelsea - have gone on to win the title.

Or is it same old, same old?

It's all very intriguing, but then again, a quick comparison of the table this year with how it ended last season suggests little has changed.

Four of the current top six finished in the top six last season...

And the current bottom three...

Well they all just about survived last season...

And even in mid-table...

There's a familiar look to how it finished up last term, with four of the same six teams occupying the middle six positions.

So maybe the world of the Premier League hasn't been completely turned upside down just yet.