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NSWC Slalom Ranking Explanation for 1997


Calculations Used to Determine 1997 Slalom Rankings

The algorithm used to compute these rankings is the same as that used in 1996.

Here's a step-by-step explanation of the algorithm used for 1997 rankings. If you don't want to read all this, skip to the end.

0. The data used is that which is available right here, on the 1997 Race Results page.

1. Each race's data is reshuffled into the same format:

Class Name(s) Time-1 Penalty-1 Total-1 Time-2 Penalty-2 Total-2 Better-Score  Total-Score

Obviously, not all of this information is available for every race; fields which are not available from the race results are left blank.

2. The classes for each race are translated from the many names that show up in results to a list of canonical racing classes. Here's an example of part of the translation table used to do this:

	C-1		C-1
	C-1W		C-1W
	C-1W_expert	C-1W
	C-1_(A/B)	C-1
	C-1_A/B		C-1
	C-1_C/D		C-1
	C-1_Cadet	C-1
	C-1_Expert	C-1
	C-1_Jr		C-1

3. Results for classes which don't currently get ranked -- that would be open boats, recreational/plastic/cruiser decked boats, K-2, squirt boats, sit-on-tops, etc.; are dropped.

4. Scores with DNS, DNR, or DNF are interpreted numerically -- this is just used to gather race statistics. Speaking of which, statistics for every race used in rankings are available.

5. If a race was scored with 2 seconds for touches/50 seconds for misses, nothing happens in this pass. But if it was scored with 5 seconds/50 seconds, the penalties are recalculated to the 2/50 system.

6. Every paddler's name is converted to canonical form, which I've hopefully spelled correctly. Here's an example:

	Carleton Goold		Goold, Carleton
	Carleton Gould		Goold, Carleton
	Carlton Gould		Goold, Carleton
	Goold, C		Goold, Carleton
	Goold, Carlton		Goold, Carleton
	Gould, Carleton		Goold, Carleton

7. Every race result is converted into this form:

Class=Name Score Ratio

where "Score" is their combined-run total score for the race, and "Ratio" is the ratio of their score to the best-score-of-the-day. For example, from the Riversport Slalom:

K-1W=Thomas,_Natalie	471.65	1.904
K-1W=Potochny,_Evy	462.75	1.868
K-1W=Gelblat,_Renee	531.46	2.145
K-1W=Hearn,_Cathy	270.49	1.092
K-1W=Weld,_Kara		272.07	1.098
K-1W=Beakes,_Nancy	317.22	1.280
Boats which did not complete two runs are dropped at this point.

8. The ratio from the previous pass is inverted to give a competitor's race ratio: this number reflects how far off they were from the best-score-of-the-day. (The boat with the best score of the day has a race ratio of 1.0.) Two lookups happen: last year's rank class (A, B, C, D or Unranked), and membership on the national A team. (The reason for this is that the strength-of-field assignment is based on this.)

K-1W=Thomas,_Natalie	0.525	C
K-1W=Potochny,_Evy	0.535	U
K-1W=Gelblat,_Renee	0.466	C
K-1W=Hearn,_Cathy	0.916	ATEAM
K-1W=Weld,_Kara		0.911	ATEAM
K-1W=Beakes,_Nancy	0.781	B
In the case of boats which competed in the same race class more than once (e.g. K-1 Masters and K-1) only the better of those two results is used.

9. Each race result is weighted by the race weight; the race weight is given by

(Field Strength + Importance Factor)
where field strength and importance factor both have maximum values of 10; thus the race weight has a maximum value of 1.0. The table of assigned field strength and importance factors, along with the criteria used to make these assignments, is here. Continuing the example above, and using Riversport's field strength of 9 and importance factor of 5:
K-1W=Thomas,_Natalie	0.367
K-1W=Potochny,_Evy	0.374
K-1W=Gelblat,_Renee	0.326
K-1W=Hearn,_Cathy	0.641
K-1W=Weld,_Kara		0.638
K-1W=Beakes,_Nancy	0.547
This number is a competitor's race weight: think of it as "how much credit you get for doing this well at this race against this competition".

10. All results from all races are combined. If a paddler has done more than three races, their best (highest) three race weights are selected. If a paddler has done only two races, they're assessed a 5% penalty; if only one race, a 10% penalty. These results are then averaged to give the competitor's rank ratio. Same example as before:

K-1W=Thomas,_Natalie	0.350	Bellefonte,Riversport
K-1W=Potochny,_Evy	0.366	Lehigh,Riversport,Bellefonte
K-1W=Gelblat,_Renee	0.369	Lehigh,Codorus,Farmington
K-1W=Hearn,_Cathy	0.841	Trials-3,Trials-2,Nationals
K-1W=Weld,_Kara		0.824	Trials-3,Trials-2,Nationals
K-1W=Beakes,_Nancy	0.654	Trials-2,Trials-1,NOC-DBH-2

11. The results are sorted by rank ratio and separated by racing class. Each boat's percentile rank within its class is assigned, based on the boat having a value of 100.0. Letter classes (A,B,C,D) are assigned based on percentile rank. Two more lookup tables are used: one to assign agegroups (e.g. Jr, Sr, Ms) and one to mark non-US paddlers.

Here's the table used to decide the assignment of letter classes based on the percentile rank:

"A" Ranked		85% to 100%
"B" Ranked		65% to 84%
"C" Ranked		40% to 64%
"D" Ranked		below 40%

Note 1: Agegroups are provided for informational purposes only and have no impact on rankings.

Note 2: The presence of non-US paddlers also has no impact on rankings, since the breakpoints for class assignments as well as the cutoff for automatic admission to Team Trials are assigned on a percentile basis, not on the number of boats.

12. That's it. Please note that although all the calculations were done to several decimal places, that does not mean that rankings are accurate to that degree. For example, the difference between a rank ratio of .453 and .456 falls well within the variability of manual timing systems.

Also, please note that paddlers who did well at important races with high field strength numbers may be ranked ahead of paddlers who beat them head-to-head.

For those of you who want the techie details, all the scripts are written in Perl and run on a Unix system.


The overall formula that was used is:
best score of race   (field strength + importance factor)
------------------ X ------------------------------------ X penalty
competitor's score                   20
where the field strength and importance are assigned from this table:
Factor PointsField Strength (fastest times)Importance of Race
104 National "A" Team athletesOlympic/National Team Trials
U.S. Nationals
93 National "A" Team athletesCIWS Finals
Junior Trials
Jr/Sr/Ms Nationals
82 National "A" Team athletesCIWS Qualifiers
Junior Olympics
71 National "A" Team athleteTeam Trials Qualifier/USOF Qualifiers
Mid-America Series
6"A" ranked athleteDivisional Championships
Major Cup Series, Major Double Headers
Junior Olympic Qualifiers
5"B" ranked athleteOther Local/Regional Races
C-D Race Series
4"C" ranked athleteCitizens Races
2"D" ranked athleteFlatwater/Pool/Jiffy Slaloms
(Any race falling into multiple categories in the table above is assigned the factor from the highest category.)

The penalty (see step 10 above) is 1.0 for any boat doing >= 3 races, .95 for any boat doing 2 races, .9 for any boat doing 1 race. (See step 10 above.)