Full Merge? Power Merge? What? Why?


Note: This article is mostly a republication of an article that appeared on the Colorado site after Colorado's state meet. Lots of people in Colorado had similar questions to the ones I'm getting from folks in New Mexico.

I've had a few e-mails from folks wondering what merges and power merges are about. Here's a quick discussion about all of that.

A merge is simply a combination of all the results from a multi-division meet. When you score this you get a picture, with some caveats that we'll discuss below, of how this meet would have turned out if all the divisions had run together.

This technique is used a lot when considering teams for inclusion in meets like Nike Cross Regionals - Southwest.

But, a simple full merge is typically very large and unwieldy. The "penalties" for lagging scoring runners in a full merge can be dramatic. So, to rectify that situation, a full merge is usually broken down into what's called a power merge. A power merge removes all the teams from the analysis except for somewhere around the top 20 teams. When deciding how many teams to include in a power merge, you typically look for a large, natural break in the team scores near 20 and make the cut there.

At this point, you eliminate all other teams (did I mention you don't want to try this without a computer and software suited to the purpose?) and then rescore the reduced meet. At this point, you have a fairly realistic picture of how the top teams in the meet would have scored against one another had they all been running in the same division. This works well because something like 20 teams seems to be the preferred meet size for a championship meet (though you can find championship meets both larger and smaller than that). 

Either a full merge or a power merge will frequently reverse the order of teams that ran against each other in the same race. While not necessarily desirable, it illustrates the fact that the scoring of a cross country meet does vary according to field size and strength of competition. That's not very surprising to folks who've spent a lot of time looking critically at meet results.

In case you haven't seen them yet, here are the merges for the New Mexico state meet results:

Boys Full Merge

Boys Power Merge

Girls Full Merge

Girls Power Merge 

For all of their natural allure, merged results need to be taken with a bit of caution. Several assumptions are implicit in a merged set of results. One assumption is that weather conditions (temperature, wind speed and direction, barometric pressure, humidity, etc.) were the same from race to race. Another assumption is that a team in the 3A race, for example, would have run just the same way in the 4A race. Probably not, but there is no opportunity to rerun the races, so we make the assumption, anyway.

With respect to the weather conditions on Saturday, the most significant difference between the races were the elevated winds for the 5A girls race. Barometric pressures were low to start the day and stayed relatively low throughout the day without any great changes. Temperatures also remained fairly constant through the day, though there were probably a few girls in the 4A and 3A races who may have felt a little overdressed when the sun came out for extended periods during the races.