The transfer window is upon us once again, and if recent sales tell us anything it's that strikers continue to be the highest priced players in the game.

Napoli sold Edinson Cavani to Paris Saint-Germain FC for £55 million and replaced him with Real Madrid's Gonzalo Higuain for £40 million. According to a vast number of sources, the Daily Star being one of them, Arsenal are being linked with a whole host of strikers with big-money moves and Manchester City have snapped up Alvaro Negredo and Stevan Jovetic for the princely sum of £39 million according to The Sun.

It would seem that strikers make the transfer market go around.

One thing that any transfer window can guarantee is that money will be well spent—it will also be wasted in equal measure. Strikers and creative midfielders will always be over priced. Goalkeepers and defenders will continue to be underrated and water-carriers will barely even get a mention.

Yet, defenders, goalkeepers and defensive midfielders provide the backbone to all teams. They are essential elements to any championship-winning side. 

The old adage that strikers win matches and that defenders win leagues, seems to get lost every time a transfer window opens.

Defensive players are often misunderstood by fans, coaches and managers alike. They do the nuts and bolts parts of the game without fuss. Defensive qualities like positional play, marking and organizational skills have not translated well to television never mind to statistical pages, and therefore attract less attention from the untrained eye.

Even then, defensive statistics like tackling and interceptions are crude devices and often misunderstood. For example, a player with superb positional play may not have to make a single tackle or interception during an entire game. Whereas a player without these skills could make numerous tackles and interceptions due to the fact that they are in the wrong place at the right time.

Add a few goals or David Beckham-like passes and you have the perfect ingredients for what many, wrongly, regard as a world-class defender. 

Defenders do their best work away from the madding crowds and cameras. They take up angles and control spaces. They often make the center-forward's mind up for them by taking a simple step to the right or left as they are marking them. Then, when the opponent's goal-scoring chance fails, it is usually put down to bad finishing by commentators and analysts rather than good defense forcing a bad shooting-angle in the first place. 

For a forward it is much easier to gain recognition from the the media and fans. That's because so much of how we grade and rate players is goals related. Defenders are even deemed better players if they can add a couple of goals or assists to their season.

This, again, can actually turn out to be the complete opposite. A defender who scores a large amount of goals, or who contributes a large amount of assists, could be a gambler without any defensive positional skills.

Media-grabbing mediocre strikers who can net 10 goals a season are most transferred far in excess of top-class defenders. 

This can be seen in the Premier League's transfers during the 2010-11 season.

Fernando Torres was easily the most expensive player that year with his €58.4 million transfer. Forwards and attacking midfielders dominated the highest transfer fees that season.

Darren Bent was sold to Aston Villa for €21.5 million, Nikola Zigic joined Birmingham City for €7.2 million, and Luis Suarez and Andy Carroll joined Liverpool to replace Torres for €26.5 million and €41.5 million respectively. James Milner, Yaya Toure, David Silva and Edin Dzeko and Mario Balotelli all joined Manchester City for a combined fee of almost €150 million.

Each player named above is an attacker of sorts.

David Luiz, hardly the greatest advertisement for a top-class defender in 2011, actually turned out to be the most expensive defender in the EPL that season at €25 million.

After that you really have to look hard to find further defensive transfers. Jean Beausejour's €4.8 million  transfer from Club America to Birmingham is actually the fourth-highest defensive transfer of 2010-11 and the 25th highest overall.

The graph, from Why England Lose and Other Curious Football Phenomena Explained by Simon Kuper and Stefan Szymanski, below shows that Premier League finishing position is more related to wages spent than transfer fees.

This shows a couple of factors worth considering. Strikers may win matches and defenders may win league titles, but only one team can win a league at any one time. Most EPL sides have no chance of winning the league title and therefore invest little in defenders.

Add in the fact that the average job-lifespan of a manager in the Premier League is just 1.66 seasons and you can see why strikers are so important—most managers live from game to game.

Clubs and managers will therefore gamble on strikers like they will with no other position on the pitch.

Take Torres as an almost perfect example. The Spaniard was transferred to Chelsea from Liverpool for $79 million in 2011 without prior consideration to his style as a player or to the playing style of his new team.

Torres was signed on past performances instead of what he could offer in the future. This is borne out in his goals-to-games rate. At Liverpool, the striker scored 65 goals in 102 EPL games. Since joining Chelsea he had scored just 15 goals in 82 matches.

When Roman Abramovich splurged his millions, he thought he was buying a striker who would fit into any team. Torres, at Liverpool, played in a side that was built completely around him. Rafael Benitez's counter-attacking philosophy relied heavily upon Torres, his pace, strength and ability to read through balls. He was, at his best, a center-forward who lived on the shoulder of the last defender.

Chelsea on the other hand were a far different beast to Liverpool. Carlo Ancelotti's side were a swift possession-based attacking side who used support midfielders in the final third to great effect. Here, Torres found two major problems. The first was that he was no longer the lone forward, the second was that his pace and power were negated as Chelsea rarely countered into space like Liverpool.

The end result was a hugely expensive gamble that has yet to fully pay off on the pitch.

Off the pitch, however, Torres has paid a huge chunk of his transfer fee back.

Of the top-10 transfer fees of all time, eight players are forwards and the other two are creative midfielders who did their best work in the final third of the field. These players command the highest transfer fees for a couple of reasons.

Not only are they some of the best players to ever grace the game, they are also some of the highest paid and most marketable.

A simple fact about football is that defenders are not only undervalued in the transfer market, they are also undervalued by fans. Cristiano Ronaldo and Lionel Messi jerseys far outsell the likes of Pepe's or Carles Puyol. Supporters like to be linked with the players they worship and the majority of jerseys sold are those of forwards and creative players.

The only time a defender's jersey sells is when he has reached cult-status. This often takes an entire career and even then the sales figures will be modest.

This theory is backed up by the figures released by Sporting ID to the Premier League's official website during the 2012-13 season. The figures, concerning EPL jersey sales in North America clearly show that forwards are far more popular with fans than defenders. Of the top-10 selling jerseys during the 2012-13 season, not one was a defender. 

If anything, the only anomaly was Tottenham's Clint Dempsey featuring so high. Had the sales accounted for Asia or Europe there can be little doubt that the American international would not have featured so highly. Kitbag's figures (h/t the Daily Mail) for UK sales verify this and also reflect fans' penchant for strikers jerseys.

In defence of strikers, an ironic turn of phrase, their skill-set is more difficult to master than defensive skills. So much of what forwards do is instinctive and impulsive. 

Creative skills do not come naturally to most players, and passing, composure in front of goal and dribbling can be difficult to learn—and near impossible to master.

In Tony Cascarino's superb biography, Full Time, the Irish international explains "the voice" that all strikers hear. The voice, as anyone who has even put on a pair of boots can attest, is self-doubt, insecurity and hesitancy all rolled into one little hateful ball.

While many defensive players suffer from similar afflictions, they do not carry the weight and burden of victory on their shoulders like forwards do.

Forwards must master this self-doubt and conquer it into submission because once it gains hold their career could be finished. Again, look at Torres' body-language since joining Chelsea. He is clearly a player struggling with self-doubt.

Conquering one's fears may just be the greatest skill any footballer can possess—be they defenders or attackers.

Top-class strikers learn to adapt to this fear from an early age. They must if they want to score goals. As any player knows there is nothing worse in football than breaking through only to be told by yourself that you won't score.

The very best forwards have beaten this voice into submission. It is not a factor in their game. The next best players can curtail it from time to time but in the end it always comes back and manifests itself in inconsistency and a lack of goals.

The end result is that strikers will always cost more than defenders because they basically score goals. Goals mean points and points mean jobs to lower-level managers. At the highest level, goals mean potential trophies and guaranteed merchandise.

Add everything together and you have a perfect concoction for any negotiating agent.

You can follow me on Twitter @WillieGannon. 

And listen to me on the Hold the Back Page podcast.