Pricing Method

QUESTION

I am relatively new to this horse racing stuff. I have only been at it for a couple of years but I been pretty serious keeping records and during this time I spent much time reading and reading and studying. I have just started to try to do my own ratings but I have struck a snag in that I am not quite sure how to convert my ratings to prices. The method I have started using is probably not right. Simply sum the ratings then divide each individual rating by the sum. So if the total sum was 500 and my top pick was 250 that would 50% so a $2:00 chance. What I have found by doing it this way my top pick is probably too long. It is often a high $3 or low $4 chance when it probably should be high $2 or low $3.

Could you please offer me some advice in resolving this dilemma as there must be a way to address. Someone said one of Don Scotts books had a table in it so I will try to find a copy of his book.

ANSWER

you may not be familiar with imperial odds. they evolved with the business of bookmaking and line up (amazingly) with the normal distribution of probability. bookmaking boards prior to decimalisation displayed an orderly roll-out of prices either side of even money ($2). they stepped in increments of an eighth of a point, thence a quarter, half, and whole out to 16/1 ($17): 9/8, 5/4, 11/8, 6/4, 13/8, 7/4, 15/8, 2/1 (ie eighths) 9/4, 5/2, 11/4, 3/1, 13/4, 7/2, 15/4, 4/1 (quarters) 9/2, 5/1, 11/2, 6/1, 13/2, 7/1, 15/2, 8/1 (halves) 9/1, 10/1, 11/1, 12/1, 13/1, 14/1, 15/1, 16/1 (whole points) note that each set of increments represents 8 betting turns. for me 10 rating points (5kg) equals 8 turns: horse 1 (90) = 1/1 ($2) (50%) horse 2 (80) = 2/1 ($3) (33.3%) horse 3 (70) = 4/1 ($5) (20%) horse 4 (60) = 8/1 ($9) (11.1%) horse 5 (50) = 16/1 ($17) (5.9%) however this gives me too much percentage. i need a probability of 1 or 100% and the above sums to 120.3%. so, i roll out each price the same number of bettting turns until i get back to 100% 1 = 5/4 ($2.25) 2 = 5/2 ($3.5) 3= 5/1 ($6) 4= 10/1 ($11) 5 = 20/1 ($21) (2 pt increments beyond 16/1) i've still 104%, and in practice i start with the longest-priced horse and work my way in till i reach 100% your method marks the above as follows: 1=$3.9 2=$4.4 3=$5 4=$5.8 5=$7 obviously the spread is far greater using betting turns, which is what you're looking for.