Liverpool have been the standout performers so far in this season's Premier League

At the turn of the year, Liverpool hold a dominant, perhaps insurmountable lead in the Premier League, Norwich are stranded at the bottom, while the rest either fight to get back into the title race, battle for the top four or scrap their way to safety.

But has the first half of the season gone entirely as the stats suggest it should?

BBC Sport analyses expected goals and other metrics to give an indication of which clubs may be over and under-achieving and what this might all mean for the second half of the campaign.

Let's start with the facts.

Liverpool are top of the table and deservedly so. They are European champions, world champions and seemingly on course to be English champions for the first time since 1990. Despite playing one game fewer, they have 13 more points than second-placed Leicester and 14 more than reigning champions Manchester City.

Reds boss Jurgen Klopp may not be celebrating yet but his equivalent at Manchester City, Pep Guardiola, has given up on the title, while Leicester's Brendan Rodgers has all but conceded. external-link

Norwich prop up the rest, with a total of 12 points, three fewer than 19th-placed Watford and six points from safety.

However, a table from football data experts Opta based on expected goals presents a different picture...

Premier League table based on expected goals Change from actual table P xW xD xL xGD xPts 1. Man City +1 20 15 4 1 27.7 49 2. Liverpool -1 19 14 3 2 19.6 45 3. Chelsea +1 20 12 5 3 14.5 41 4. Man Utd +1 20 11 5 4 13.4 38 5. Southampton +10 20 11 5 4 3.3 38 6. Leicester -4 20 9 6 5 9.8 33 7. Wolves 0 20 8 7 5 4.4 31 8. Burnley +5 20 9 4 7 -1.2 31 9. Everton +1 20 6 9 5 2.2 27 10. Sheff Utd -2 20 6 9 5 1.8 27 11. Tottenham -5 20 6 8 6 0.1 26 12. Brighton +2 20 7 5 8 -4.3 26 13. Watford +6 20 6 6 8 -8.5 24 14. Arsenal -2 20 5 6 9 -3.2 21 15. Crystal Palace -6 20 5 4 11 -11.8 19 16. Bournemouth 0 20 2 9 9 -8.1 15 17. Norwich +3 20 3 6 11 -13.8 15 18. West Ham -1 19 3 4 12 -12.7 13 19. Aston Villa -1 20 3 4 13 -15.0 13 20. Newcastle -9 20 1 5 14 -18.3 8

xG table explanation For the purposes of the above table a number of rules were set by Opta: If both teams have an xG of 0.5xG or less: 0-0 Draw If the highest scoring team (in terms of xG) has more than 0.5xG and less than 1.1xG, they win if the xG difference is bigger than 0.3xG If the highest scoring team (in terms of xG) has more than 1.1xG but less than 1.5xG, they win if xG difference is bigger than 0.4xG If the highest scoring team (in terms of xG) has more than 1.5xG, they win if the xG difference is bigger than 0.5xG

Before some fans go on social media to howl about the injustice of it all, we fully acknowledge that expected goals is not a perfect model, nor is it a universal one (you can read more about it here).

There are other factors to consider - luck, injuries, human error and a VAR system in its infancy have all contributed to results in the first half of the season and will continue to do so in the second.

The January transfer window also enables sides to refresh their resources with the aim of enhancing efficiency.

In addition, assessing sides on one half of a season is made problematic for the fact some have played more away games at tougher opponents than others.

As we are one game into the return set of fixtures, some teams have faced tougher opponents twice already, with Leicester having played Liverpool twice, while Wolves have had two games against Manchester City (although they did impressively win both).

However, there are some interesting strands to pick at from the above table.

Most notable is Manchester City sitting top, four points above Liverpool. This represents a considerable points swing from the actual table, with City's expected points tally eight better than their real total, while the Reds are 10 points worse off.

The biggest positional changes from the actual table put Southampton in fifth as opposed to their actual position of 15th and Newcastle bottom instead of 11th. Other big movers are Burnley (up five places to eighth), Crystal Palace (down six to 15th) and Watford (out of the relegation zone and up to 13th).

But at which end of the pitch are sides excelling or letting themselves down?

Attacking/defensive prowess

The first graphic below illustrates each side's attacking prowess, showing the number of big chances created per game on one axis and their conversion rate of these on the other.

Opta's definition of a big chance: A situation where a player should reasonably be expected to score, usually in a one-on-one scenario or from very close range when the ball has a clear path to goal and there is low to moderate pressure on the shooter. Penalties are always considered big chances.

The numbers below relate to each side's current position in the table.

The second graphic below illustrates each side's performance at the other end, showing the number of big chances they concede per game and their opponents' conversion rate of these chances.

The rest of the season?

It is very unlikely we are going to see a change at the very top of the table, with Liverpool's current advantage too much for Manchester City, who are the division's most creative side but not as clinical as they need to be while also conceding more big chances per game than nine other sides.

Leicester are impressive in both defence and attack, but rely heavily on the continued prolific goalscoring form of Jamie Vardy - a striker who is impressively outperforming his own personal expected goals by more than five.

Best performing Premier League strikers - actual goals v expected goals Player Club Goals (non-penalty) xG (non-penalty) Performance Jamie Vardy Leicester 14 8.88 +5.12 Pierre-Emerick Aubameyang Arsenal 12 7.64 +4.36 Danny Ings Southampton 12 8.23 +3.77 Harry Kane Tottenham 9 5.4 +3.6 Tammy Abraham Chelsea 12 9.41 +2.59 Sadio Mane Liverpool 10 7.58 +2.42 Teemu Pukki Norwich 9 6.76 +2.24

The race for the top four is more open, with Chelsea looking vulnerable unless they arrest their woeful conversion rate from what is a healthy number of big chances, which is a failing that manager Frank Lampard says the club intend to rectify in January.

Manchester United will be firmly in the mix, especially if they can make more of a high number of good chances created. Their defensive performance is impressive and will improve further if goalkeeper David de Gea can recapture his best form.

By contrast, Tottenham will be encouraged by their ruthlessness in front of goal, but need more ammunition from their creative players. Spurs can also point to an unusually high concession rate from the big chances they have faced - something Hugo Lloris' return from injury should help improve.

Best performing goalkeepers - actual goals conceded v expected goals Player Club Goals conceded xGOT conceded* Goals prevented Hugo Lloris Tottenham 8 11.7 3.70 Martin Dubravka Newcastle 30 33.66 3.66 Vicente Guaita Crystal Palace 18 21.49 3.49 Dean Henderson Sheff Utd 16 18.82 2.82 Ben Foster Watford 33 35.55 2.55

Worst performing goalkeepers - actual goals conceded v expected goals Player Club Goals conceded xGOT conceded* Goals allowed Kepa Arrizabalaga Chelsea 28 19.58 8.42 Angus Gunn Southampton 25 17.62 7.38 Nick Pope Burnley 32 25.49 6.51 Tom Heaton Aston Villa 34 28.05 5.95 Paulo Gazzaniga Tottenham 21 16.16 4.84

*Expected Goals on Target model is built on historical on-target shots and includes the original xG of the shot but also the goalmouth location where the shot ended up (read more here). external-link

At the other end, West Ham have the biggest concerns and will be hoping new manager David Moyes can correct a woeful defensive performance in which they have conceded by far the most big chances, otherwise they are at serious risk of relegation.

This is especially the case with Watford improving so dramatically under Nigel Pearson - the Hornets having collected 44% of their league points and scored 40% of this season's top-flight goals in the last three games alone.

Of the teams not currently in or around the relegation zone, Crystal Palace and Newcastle look most at threat of being dragged in. The two have produced the lowest number of quality goalscoring chances and both are conceding more than two big opportunities per game so far.

As you can see above, their goalkeepers are two of the best performing against their expected goals on target conceded.