Answer this:

if the Grand National is such a lottery then why do only a handful of horses have a realistic chance of winning the race every year? Yes, Foinavon demonstrated in 1967 that just about any horse can cross the line first if - and only if - half the field is removed at a single fence. But that's happened once in history. It was a random act, a moment of chaos. You get that with 40 horses in a field jumping over five-and-a half-foot fences.

Cynics could say that a similar chaos can describe what happened to Auroras Encore and Ryan Mania last year, winners of the race at anything between 66 and 120/1 before the off.

The Tenner Bet takes a different view. The bookmakers and the general public at large slept in on Auroras Encore. The horse had all the traits required to win a Grand National, it was after all second by a short head in the Scottish version at Ayr just a year earlier. I know this story so well because I backed it just as I have backed 13 winners of the National in the past 25 years. The purists will say it's a not a proper race - and to some extent - they have a point. For example, Walkon will be a popular pick on Merseyside this weekend. Liverpool are flying in the Barclays Premier League, Aintree is a 10-minute drive away from Anfield. Aha, the stars shall align. Well, no, they won't. Walkon has about as much chance of winning the Grand National as Hearts have of staving off relegation. There are indisputable reasons for this and they are backed by years of statistical trends:

WINS OVER three miles

Grand National winners do not prevail in the race if they have not succeeded over long distances. The general rule says three miles is that mark. The last horse to do it was Gay Trip in 1970 while Seabass, joint-favourite two years ago, had only won over two and a half miles. That's a big negative for Walkon, Last Time D'albain and Buckers Bridge in this year's race.

AGE 9-12

Younger horses have a poor record because they have more speed than stamina. The eight-year-olds in the race fall into this category and again we have statistical proof to back our claims. Last year, none of the first six home was under the age of nine. In 2011, the first 10 home were aged between nine and 11. It's a black mark against the seven-year-old Kruzhlinin, Double Seven, Rocky Creek, Vintage Star, Vesper Bell, Our Father and Twirling Magnet. At the other end of the age scale, it's bad news for those who fancy Tidal Bay and Swing Bill.

WEIGHT

Anything carrying 11st 6lb or more should be struck off your list, too. However, changes to the layout of the track and some of the fences has shown an inclination towards horses with more weight coming into the reckoning than was previously the case. Nevertheless, the burden saddled by 2011 Gold Cup winner Long Run, Hunt Ball and Triolo D'Alene should be insurmountable given what others are carrying.

CHASE RUNS

It stands to reason that horses with more experience over national hunt fences will fare better than those without it. The national fences are the most difficult in the sport and there can be no substitute for the real thing. Ten from 10 previous winners have all had 10 runs or more over fences. Strike Colbert Station, Hawkes Point, Mountainous, Rose Of The Moon and Once In A Milan off your list.

CLASS

Good horses, but not necessarily great horses, win the National. By extension, poor horses do not feature in the shake-up. Runners with proven ability should be on your list and those without it should not. So anything that hasn't won a chase worth at least £17,000 isn't going to win one with a first prize of half a million. Get rid of Golan Way and Across The Bay.

THE SELECTION

That leaves 18 remaining horses and if that appears daunting the list can very quickly be halved again by looking at factors such as career falls and days since last run. I usually apply a tolerance of two to the first attribute since it's fairly clear that horses that are more prone to mistakes may struggle. That gets rid of Battle Group and The Rainbow Hunter. The latter factor is slightly more difficult to predict.

Horses that had tough races at Cheltenham have tended to find the Aintree marathon, which comes less than a month later, a bit of a slog but in recent years Silver Birch, Bindaree and Don't Push It have won the National after racing at the Festival. Teaforthree was one of my bigger bets in the National last year and I have a hard time deserting the Rebecca Curtis-trained horse and so it might just be the exception in this case not least because of an excellent run in the race in 2013. For the rest, though, it claims Shakalakaboomboom, Balthazar King, The Package and Big Shu. That leaves a double-figure list which has been narrowed down by a combination of other less obvious factors.

Bet365 are offering half stakes back on all each-way bets and that is my idea of a decent deal not least with a heavy liability on the race with four horses selected.

Burton Port (16/1), which like all good National contenders had a run over hurdles earlier in the season, is the pick with nods to Teaforthree (9/1), and Lion Na Bearnai (33/1) and Pineau De Re (22/1).