What is a Speed Rating? - Quick Explanation:
Here is a brief step-by-step explanation of how a speed rating is made:
(1) Get the results of a cross country invitational (the actual race times), as deep as possible ... (if enough sequential race times are not available, it may be impossible to make a speed rating for that race).
(2) Use the actual race times to determine how fast or how slow the race was compared to a "standard race" ... For example, I might determine the race was 15 seconds slower or 15 seconds faster than a standard race ... I can use several different statistically methods to determine how fast or how slow the race was ... this number of seconds is the race correction.
Updated definition of a Standard race ... I have a library of "standard races" ... Usually, my first choice is to compare the race being evaluated to the same race from the previous years (I have already determined their relative speed) ... Other standard races for comparison include any races of similar overall quality ... I typically use multiple races for the comparison.
(3) Whenever possible, derive a separate race correction based solely on the individual runners in the race ... I use my individual runner databases to make statistical comparisons between their previous speed ratings and the final times of current race ... This yields a second race correction to compare to the standard race correction from above ... usually they are similar ... I derive a final race correction based on both.
(4) Add or subtract the final race correction number from the actual race times ... for example, if the race correction number is +15 seconds (meaning the race was 15 seconds slower on average than the standard race), I then subtract 15 seconds from all the actual race times to get "corrected" race times ... (as an example, if the actual race time was 20:00.0, the corrected race time would be 19:45.0).
(5) I could just post the corrected race times ... but, for comparison purposes, I find it easier to convert the corrected race time to a simple number (a speed rating) ...
Speed Rating = (1560 - (actual race time in seconds) - (course correction factor)) / 3
where 1560 is the number of seconds in 26 minutes ... 26 minutes is used because it corresponds to zero in the standard race ... the course correction factor is how fast or slow (in seconds) a race course is in relation to a standard course ... the entire expression is divided by 3 because I decided one point equals three seconds in this method.
Bottom-Line ... a speed rating is just a corrected race time (that's all) ... it allows speed comparison of any race to another race ... it's nothing more than that!
My Articles-Page contains links to several articles that describe my speed ranking method and speed ratings more fully.
One article to view: "Early Season Speed Ratings and a Brief Overview of Speed Ratings"
How Is It Possible? ...
Here's a common question I receive ... "How is it possible to compare the speed of one race to another race, especially when you don't know who the runners are??" ... perhaps an analogy can help explain:
Consider school grades ... A, B, C, D, F ... the majority of students are "C" (average) students ... the ability of average students in one school may be different from average students in another single school (so you may not be able to compare them directly) ... But, if I take a large group of schools from central NY (small, medium and large schools; good, mediocre and poor schools) and compare it to a large group of schools from any other part of State, you'll find the "average" students (in these large groups) are roughly equivalent in ability.
Often, it is necessary to make the following assumption for XC ... the ability (race speed) of the "average" runners in a large invitational race is equal to the ability of "average" runners in a different large invitational race ... I don't need to know who the "average" runners are, only their ability as a group ... If I can identify the "average" runners (and how fast they ran), then I can approximate how fast one race is compared to another ... It's just statistical sampling, but you really need the correct sample!
Some people use charts that compare one XC course to another course (in terms of speed) ... I rarely use this method ... It may work OK sometimes, but it usually fails when the weather turns bad ... The only race course where I use this method (if the statistical methods can't be used) is the 2.5 mile course at Van Cortlandt Park - for some reason, it never seems to vary more than 10 seconds despite the weather!