We have a theory here at InsideEdge. When Cain got booked for a wicked foul on Able in the Stadium of Eden a few years back, he really started something. Well, how else do you explain the intense, almost tribal rivalries kicking off once more at derby matches all over Europe this month?

Yup, the season of bad blood is starting in earnest, with November featuring Arsenal vs Spurs, El Derby between Real Madrid and Barcelona, the Italian derby as Juventus take on Inter Milan and the Basque showdown between Real Sociedad and Athletic Bilbao. Then December brings Liverpool vs Everton and another big London clash between Arsenal and Chelsea, among a raft of derby fixtures across the rest of Europe.

Commentators and pundits often talk up the so-called derby factor when analysing these clashes, but for punters this is meaningless unless backed up by hard evidence. Is there a real or merely a perceived derby factor, to what extent does it actually influence results and under what circumstances? None of which is easy to hang specific figures on - but it's a worthwhile exercise for serious football bettors.

In fact, many derbies do follow patterns - albeit peculiar ones where form is often overturned - and understanding this can give you a significant edge. The 14 derbies analysed here are a good cross-section: a mix of city, regional and national rivalries.

The common factor is the rivalries are intense and have been renewed on a regular basis over the past decade. Which is why I've not deemed historic contests such as Manchester's derby and Newcastle vs Sunderland worthy of close consideration, as there have been significant gaps in those rivalries in recent years.

The draw factor
The big derbies are usually characterised as hard-fought, close contests with a high proportion of draws and a low number of goals. As a general rule, this stereotype is, it turns out, also backed up by the statistics. Liverpool vs Everton provides a good example of this. For the past decade Liverpool have been a better team than their city rivals, yet they have a less successful record in Merseyside derbies than would be expected.

According to my figures, the derby factor has brought a swing in Everton's favour amounting to a quarter of a point per game. As there is a sizeable gulf in class between the two teams, this has not been enough to bring Everton any more wins than would be expected, but it has reduced their number of defeats and consequently increased the number of draws. The 20 Merseyside derbies played in the Premiership over the past decade have produced ten draws - double the normal draw rate for teams of their class.

This derby conforms to all aspects of the stereotype - it has the fewest goals per game (1.95) of the 14 derbies listed in the box to the right, and consequently the highest number of low-scoring games (13 out of 20 have produced under 2.5 goals). Others fit the stereotype too:

- The North London derby between Arsenal and Spurs (ten draws out of 20, 2.15 goals per game and 11 out of 20 low-scoring games)

- The Ruhr derby in Germany between Borussia Dortmund and Schalke (11, 2.15, 12)

- The Basque derby between Real Sociedad and Athletic Bilbao (nine, 2.65, ten)

- Soccer-mad Seville's derby between Real Betis and Sevilla (nine, 2.25, ten - from 16 games)

All have a very high draw rate and, with the exception of the Basque derby, a lower than average number of goals.

Many derbies produce a high number of draws. Those 14 derbies have produced 104 draws from 268 league matches over the past decade - a rate of 39%. A level-stakes bet of £10 on the draw, even assuming stingy odds of 2/1, would have earned a profit of £440. At odds of 9/4, the profit would have been £700 - a very healthy 26% return on turnover.

Moreover, it's a system that works year in, year out, with that 26% return on turnover (at least) achieved in eight of the past ten seasons. The draw rate has varied significantly from the average in only three of the past ten seasons - in 1998/99 it was massively inflated at 58%, while last season it was down to a low of 25%. That was the first season since 1994/95 when the rate of derby draws fell below 36% and, consequently, also the first since then that had failed to produce a level-stakes profit by backing the draw.

Laying the favourite
With the derby factor often creating a more level playing field and the draw so heavily in the layers' favour, it could be assumed that laying the favoured team would make sense. The case isn't compelling, however. In our 14 derbies, 57% of the matches over the past decade have seen the underdog gain at least a share of the spoils - the average distribution per season being 12 wins for the favourite (43%), 11 draws (39%) and five wins for the underdog (18%).

The problem for layers is that the average favourite's price in a derby match is 6/5, meaning that the normal distribution of results would produce a profit of £150 if the favourite was laid to a £10 level-stake bet on the derbies featured here. Sure, it's a profit, but a measly one - especially as this figure doesn't account for commission on the exchanges.

Even with an increased stake, the potential gains from this approach don't appear to outweigh the risks. The reason is that the favourite's win rate would rise in the event of fewer draws than average - as it did last season, when favourites won 57% of the derbies featured here. This link with the draw rate means that the best way to oppose the favourite in derby matches is by backing the draw.

Derby variations
But while the draw is generally an attractive bet in derby matches, it doesn't cover all options.

Derby matches fit into three categories, as shown in the tables. As a rule of thumb, the draw rate is usually highest in well-established city derbies, while the so-called 'national derbies' (such as Manchester United vs Liverpool and Real Madrid vs Barcelona) show a tendency towards fluctuating fortunes, as well as an above-average number of goals. There are also several derbies where one team has enjoyed a long period of dominance over the other, and here too the number of goals per game is above average.

One of the most fascinating contests is the Milan derby, where another significant factor is at play: the negating of home advantage. There has been an almost even split between Milan wins, Inter wins and draws over the past decade but, more remarkably, the most common outcome has been an away win. This has been the result in nine of the past 20 meetings and is twice as prevalent as a home win.

It's a rarity even in the most one-sided matchups, and may be due to the fact that both teams play home matches at the San Siro, making ground advantage less significant than usual when it comes to their derby meetings. A similarly even split of results is evident in Rome, where both teams share the Stadio Olimpico, though in this case away wins are no more prevalent than would be expected.

The London derby factor - so long regarded as an insuperable hurdle for a capital club with title aspirations - has been laid to rest in recent years by Arsenal. They have won 39 out of 64 London derbies in seven full seasons under Arsene Wenger, with only five defeats, and have led the London mini-table in every one of those seasons.

Chelsea's record, on the other hand, conforms more to the old London derby stereotype, with valuable points dropped in their capital clashes. Last season was their best in London since 1998/99 (when they went closest to Premiership victory) but still they suffered three of their seven defeats against London clubs.

There might be some mileage still in backing against Chelsea in London derbies - even last season they failed to win three out of eight, and in the previous five seasons their win rate was never better than 50%. It should be noted, however, that their derby record looks much better once games against Arsenal, their nemesis in recent seasons, are removed.

The team that really has a history of under-performing in London derbies are Spurs, who won just nine of 44 in the five seasons up to the end of the last campaign. Although they have over-achieved at home against Arsenal - and to a certain extent away, at least by keeping games closer than would be expected - their record against the other London clubs is poor.

Old Londinium town
On the other hand, Fulham, Charlton and West Ham (when they were in the Premiership) have generally performed above themselves in London derbies. Perhaps the explanation is that the smaller clubs raise their game for every London derby, whereas the big teams see the more minor London derbies as no more important than a normal game. A good example was Chelsea's 4-2 defeat at Charlton last season, which ranked as easily Charlton's best home display of the whole campaign.

Arsenal have learned to overcome such complacency on a consistent basis, but it does not mean that they are immune to the derby factor when it comes to 'the big one' - the North London showdown with Spurs. Arsenal have been dominant at home in recent seasons - with five straight league wins - but even so Spurs have outperformed their expected points tally by an average of 0.2 points per game in all league meetings over the past decade, and have not lost at White Hart Lane since the 1998/99 season.

It is reasonable to ask why the derby factor should level the playing field, rather than exaggerating the gap between two rival teams. The simple answer is that it does not produce close matches in every case - just in the majority of them. Newcastle's dominance over Middlesbrough is an example of a derby where one team (Newcastle) performs at its usual level, but the other (Middlesbrough) drops well below it. But such cases are rare.

Bigger teams are probably more susceptible to the derby factor because they perform at a consistently high level, giving them little room for improvement even under derby conditions. Usually inferior rivals, however, have more scope to raise their game on a one-off basis, while there is also the possibility that the better team will drop their standards.

Arsenal's visit to White Hart Lane last April was a good example of the latter phenomenon. They were cruising at 2-0 up with less than half an hour to play but, with the title already won, they took their foot off the pedal and were pegged back to 2-2. Spurs' performance was slightly above average by their standards of last season but it was also significant that, according to my ratings, the result meant it was by some distance Arsenal's worst display of their unbeaten league campaign.