Percent Back in General
Percent Back is a useful way to compare a skier’s races against one another.  Because terrain, distance and snow conditions vary, it is not possible to compare our times from race to race.  Because the competition at different races can vary widely, comparing our places from race to race can be misleading.
Percent back measures how one skier’s time compares to the race leaders in relative terms.  Because it is a comparative percentage of race time, the race distance and time is irrelevant, allowing us to compare a 5K classic race at Hillside to a 10K skate race at Mirror Lake, for example.
Percent back measures by what percentage each skier’s time differs from the average of the top 5 skiers’ times for a given race.  So if the top 5 finishers’ average race time was 10 minutes and my time was 20 minutes, my percent back would be 100%.  If my time was 11 minutes, my percent back would be 10%.  The smaller the percentage, the closer a skier’s time to the top 5 times, so smaller numbers are better.  (Note: sometimes, percents back are calculated from the average of the top 3 times, but I have used the top 5.)
Because we use an average of the top 5 times, percent back is relatively unaffected by the presence, absence and results of specific competitors in a particular race.  So if Fiona, who usually finishes near the top of the pack, doesn’t compete one weekend, my place might be higher but my percent back should be about the same.  Similarly, if someone else has a freakishly fast or slow race, it won’t affect my percent back.  For this reason, it is much better to compare races using percent back instead of looking at the results of specific competitors.  If Kenneth beats Anders by a minute in one race, but Anders beats Kenneth by a minute in the next race, this doesn’t mean that Kenneth is slower than he used to be.  His percents back might be very consistent, telling him that Anders is the fickle one.
Because percent back is based on time, not place, it is not affected by the size of the field.  If I get 10th place in a race of 30 people but 70th place in a race of 150, percent back is the only real way to fairly compare my two races.  My percents back for the two races could be the same, or my 70th place finish might even be better in relative terms.  This is especially relevant to those skiers who have switched racing categories a lot and find their places varying, i.e. someone who skied in the D race one weekend, and the B race another weekend.

Notes on the specific information here:
1.	The information is organized by skier, not by race, because the idea is to compare each skier’s races against one another to see general trends in that person’s racing season.
2.	The places I have listed in the 3rd column have letters after them.  Those letters stand for which category the skier competed in.  “AG” means “A Girls” and “DB” means “D Boys” etc.
3.	There are 3 columns of percents back.  The first is the percent back from the top 5 skiers in the A race.  The second is from the top 5 skiers in the B race.  Skiers who competed in the A race won’t have anything listed in that second column.  The last column is the percent back from the top 5 skiers in the C race.  I calculated these values ONLY for those who competed in the boys C, D, and E race of the Chugiak Stampede.  Those skiers skied a different course from the boys A and B race, so it wasn’t possible to calculate their percents back from the leaders of those categories.
4.	If you see a negative percent back next to your name, it means your time was faster than the average time of the top 5 skiers in that race.  Congratulations!
5.	Most peoples’ percents back were lower (better) at the Chugiak Stampede.  This could mean that everybody on the team suddenly got faster, but it’s probably because a large number of top skiers, who just returned from U.S. Nationals, did not race.
6.	I did not calculate percents back for the Bartlett race due to the complex relay format.  It would have given me a huge headache.