After much pottering around,it seems that winners keep on winning and losers just keep on losing.
If you wish to narrow fields down to make it easier and probably more profittable,get rid of the half of the field with the lowest win percentage.
I'm sure someone has played with this idea.Any comment?

Gets alittle more indepth than that i think Moee.. Horses could be running good places and nearing a win and you'd miss out,usually some value in these horses as well.
Crown Princess on the weekend was a good example and Wager ran a few seconds before eventually winning..with all the video i watch i'd love to eliminate half the field i'm studying but if i did i'd miss out on some good winners.

Doesn't work Moe.

The ones that keep winning will then be priced as favourites. Favourites are short, tend to attract action from the mug punter, and therefore aren't usually a good bet.

For horses and dogs I'd think that the middle-upper middle is probally where the value usually is. Eg in a 12 horse race, the horses ranked 3-7.

Attracting money from the mug punter seems to be where my system is directing my selections.
Work on this.
If the starting price generally predicts the starters chances,then by backing the favourite in every race,I should lose about 17% or so of my investment.
If I were more selective in which favourites I backed,then That 17 % would go up a little bit,or down a little bit.
Well my selections are nearly always favourites and are currently losing around 90% on turnover.
What on earth have I come across here?

90%?? Alot of bad luck. At TAB prices you should lose at a rate of 7.5%. Backing favourites you should lose slightly more, since bookies tend to shade favourites.

Mo, since faves usually attract the mug punter, doesn't it make sense that it's more likely value is on the other side?

Look at home dogs, home faves and away dogs. Stay away from away faves.

Mr J wrote, "...since faves usually attract the mug punter, doesn't it make sense that it's more likely value is on the other side?"

In horse racing (throughout the world except Hong Kong) the mugs back anything but the Favourite. To illustrate consider the following numbers:

Sat Metro races - last three years, NSW TAB divs

SP under 11.0 SP over 11.1

5477 races 5448 races
4370 winners 1107 winners
SR 79.8% SR 20.3%
LoT 15.0% LoT 26.7%

Just backing the Favourite reduces the LoT another couple of % points.

Which section of the market are the mugs slothing around in? Which section of the market do you want to concentrate your efforts on?

Sports punting can be different. You are familiar with the Football-Data site that proved backing short priced Soccer teams (<1.3) was profitable irrespective of form, injuries, condidtions, H/A etc etc etc so certain sections of Sports betting also exhibit a fav-longshot bias.

Good point. Maybe in horses the mugs look for the big payoff more than the 'sure thing'. I can really only offer an informed opinion on sports.

"attract the mug punter, doesn't it make sense that it's more likely value is on the other side?"

This is my main point to Mo. Look at the exact opposite of what the mug punter is likely to bet, and more often than not that's where the value is (if there is value to be had).

"Look at home dogs, home faves and away dogs. Stay away from away faves."

I said this because there are quite a few subsets where favourites are a good bet (like you pointed out), but they are much more likely to be a home fave than an away fave.

Each sport obviously has to be looked at seperately though, eg:
away dogs in MLB
home dogs in nfl
all dogs in NRL
home teams in AFL

Dear Doctor,
Even though the roughies are showing a poorer return than the favourites,I'm sure if I attempted the challenge,I could quite easily improve that percentage loss by eliminating many of those selections.
Not so sure if I could improve the more favoured runners to less than a 15% loss.
Statistics can always be misleading,and interpreting correctly what the figures are really saying can be a pathway to the edge we all need.

Mo,A simple but effective way to trim down any race is to only consider those runners on the first 5 lines of the betting.I do tend to agree wiyh your statement that figures can at times be somewhat misleading,however having said that it has statistically been proven since the year dot that this group of horses win approximately 80% of all races run.Roughies do not win that many races ,neither do battling trainers or lower echelon jockeys.If you are selective with your races,you can make this work for you.My only reccommendation is NOT to take any notice of the prepost prices,just the horses on the first 5 lines.If there is more than 1 nag on any given line,consider them all,but don't go beyond the 5th line.Then do your own form study,best trainer,best jockey,barrier draw,recent form,days since last start,etc. and narrow it down to your outright selection.Then do your own ratings,or subscribe to a ratings service,or utilise the free ratings on this site,which have personally to be very good,and they are free.Then convert your ratings to prices,and back the overlays.This method will take you away from the "herd"mentality.I Personally like to concentrate on races where IMO the fav does not warrant being fav.Another stat that has stood the test of time.....favs win approx 30% ofall races.Nothing like stating the obvious,but on the obverse side of the coin,that means they lose 70% of the time,and that is the % advantage that I am trying to exploit.I have my own criteria that I use to eliminate "false"favs,but they are quite rigorous and I am not prepared to post them at this point in time.Also have a very good method for quinellas incorporated with this.Contrary to popular opinion THERE is value to be had in quins,if you bet to prices(yours)and there are overlays galore,especially in the 10/1 or less price range.If anyone is interested in quinella betting,I will start a quinella thread further down the track.
cheers

You are right purpleheart - Quinellas are very good value when considering shorter priced runners - far better value than trifectas.