Arsenal's bright start to the new league campaign was built upon their rarely seen before defensive solidity, but shorn of confidence further forward, slowly but surely any modicum of consistency at the back has crumbled away into dust - but is this merely a blip or a return to the norm for Arsene Wenger's side.

Arsenal have developed a worrying trend in the past five years of conceding more goals in the league than the previous year before. In 2007-8 it was 31 goals, in 2008-9 it was 37 goals, in 2009-10 it was 41 goals and in 2010-11 it was 43 goals, while last term they let in 49 on their way to finishing third. It's become abundantly clear where the fault lies and given that Arsene Wenger recruited a centre-back in each of the summer transfer windows prior to this year's, bringing in Thomas Vermaelen, Laurent Koscielny and Per Mertesacker, and you sense that he realises it's the area where they need to improve the most.

The appointment of Steve Bould in the summer as Wenger's assistant was heralded as the dawning of a new era as he replaced Pat Rice. You see, good defender makes good defensive coach was the thinking, yet without the right ingredients to work with in the first place, you're already facing an uphill battle akin to getting blood out of a stone.

Since keeping three straight clean sheets in their opening three league games of the season against Stoke, Sunderland and Liverpool, Arsenal have kept just one in their last 14 games in their home game against QPR. They've conceded 23 goals across all competitions in those 14 games and they've let in seven in their last three games against Manchester United, Schalke and Fulham. So much for the Steve Bould effect then, and while the fawning praise was misdirected at best earlier on in the campaign, interestingly, criticism seems to be in short supply now that the reverse has happened. Good gig if you can get it, but where exactly has it all gone wrong?

Well the first signs can be traced back to the international break in October and it's slightly unfair to blame the defence completely for the amount of goals that the team are conceding, for you have to work as a unit when you are without the ball. Prior to the last round of World Cup qualifiers, Arsenal had just beaten West Ham 3-1 at Upton Park in a dominant display, yet they've won just two of their seven games since the players return.

The likes of Santi Cazorla and Mikel Arteta have struggled for rhythm, while the injury to Kieran Gibbs, an ever-present right up until the international break, has seen him confined to the sidelines with a thigh injury ever since, which was given its customarily optimistic diagnosis, which has since turned out to be woefully inaccurate, a fault which is now common practice these days in the Arsenal treatment room.

The result has seen a back four which worked well as a unit broken up and Wenger indecisive on how best to fix the problem. While it may be harsh to call Andre Santos one of the club's worst ever signings, he has been truly diabolical whenever he's stepped into the side recently; he lacks any sort of pace, positional sense, willingness to track back or sharpness in the tackle. He is a winger's absolute dream and the fact that Wenger thought it prudent to spend £6.7m on a Brazilian full-back with a reputation for being dodgy defensively, then expected him to be anything other than that when he came to the club just serves to show you what a panic buy he was.

He looks about two stone overweight and has been a liability which has prompted further shifts in personnel, with the club's captain Vermaelen pushed out to left-back against both Schalke and Fulham, but the damage has already been done and the partnership of Koscielny and Mertesacker has never been the strongest around, even when the side has been playing well.

Then comes the individual errors, with Koscielny's performance in the 2-1 defeat to Chelsea and his horror-show against Reading in the cup, not to mention Vermaelen's quite frankly awful clearance against United leading to van Persie's opener in the third minute serving as prime examples.

As a manager, you simply can't legislate for clangers like these and there's nothing much you can do about it from the touchline. When the team is playing well and the defence is on top form, mistakes like that simply don't happen, but they've only served to compound the problem at the moment.

Liverpool faced a similar issue earlier on in the campaign, when for all of their good work on the ball and further up the pitch, a sloppy mistake gifting away possession in a dangerous area often led to a goal or the concession of a match-defining penalty. It must be hugely frustrating for Wenger on the sidelines, yet he appears to have tinkered with a winning formula and made poor decisions at every turn.

Bacary Sagna has replaced the in-form at Carl Jenkinson at right-back, while Andre Santos came in at left-back. Would it not have made more sense to shift Jenkinson to the left and kept Vermaelen where he was if he wanted to ease Sagna back into the side? Koscielny has the potential to be a world-class defender on his day, yet he's been hampered by the bundling of the Santos situation and has looked uneasy and unsure whenever he's been selected since as a result.

At the moment, despite their recent struggles, the side have still conceded just 11 goals in their opening 11 league games, which when you compare it to the previous five years above, looks like a slight improvement this early on. Only Stoke and West Ham have kept more clean sheets than their tally of four, while only Manchester City and Tony Pulis' sides have shipped less goals. All is not lost, but confidence is a difficult thing to turn around and the north London derby couldn't have come at a worse time.

The much-vaunted Steve Bould effect earlier on in the season was a fallacy, but they undeniably looked a more solid, organised and confident unit. A combination of Gibbs' injury, Santos' horrific form and Sagna's return and the subsequent effect that these factors have had on Vermaelen and Koscielny has wreaked havoc. At the moment, while it may be something of a crisis of confidence, it's far from a full-blown crisis and the wobble can be corrected, but if they are to improve on the previous years' gradual defensive decline, they need to arrest the slide soon.

You can follow me on Twitter @JamesMcManus1

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