Sorry about the delay. It's a busy time for me.

Anyway...

Anthony wrote:I was wondering if you could give me your opinion regarding averaging the results I **include** from my LM. What I mean by this is that when I put someone on the LM and they hit, lets say, 12 shots. If there happens to be some outlying data (let's say a worm burner) I delete it from the data.... Also, I sometimes throw out a few of the highest and lowest shots to get info on the better shots hoping to maximize the persons decent shots without figuring in the not so good shots.

I'm hoping you could post your opinion on this when you have a chance, as to what is "mathematically or scientifically correct" regarding something like this.

Anthony,

Data analysis is an art in itself. I have taken a one-semester course on the subject (years ago), and suspect it barely scratched the surface. Here are a few thoughts on the subject:

**Median, not average** - When you take an average, you are trying to find a "central tendency" to the data. You really don't care what the mathematical average is; you want to know what the "typical" value is -- whatever that means.

If you don't have a good handle on the mechanism generating the statistical variation (and you probably don't for an arbitrary golfer's swing), then you are probably better off using the

median than the average. One nice thing about the median is that it automatically throws away outliers (you don't have to), unless outliers constitute more than half the data.

Here are a few references about the median -- how to compute it, and what it means:

**Impact tape** - Most data analysis problems present you with a bunch of numbers and ask "tell me something about this set of numbers: typical tendencies, variation, etc." But we as clubfitters are better off than that. We actually saw the shot. We know if it was a terrible swing. In short, we have more information at our disposal than just the numbers. You indicated you already make use of this "side information" (as data analysts would call it) when you talked about "worm burners".

You have another very important tool for gathering side information: impact tape. This can tell you at least as much about the quality of the hit as the LM numbers themselves. I would use it as follows:

- Start by fitting the driver to minimize the number of mishits. More specifically, find the driver that gives the best pattern on the impact tape. At this stage, you are not paying much attention to the LM except to see if the trajectory is OK (slice, hook, etc), but rather to visuals of the swing and what the impact tape is telling you. The things you are focusing on are club length, measures of heft (swingweight, MOI, total weight), grip size, etc. These affect the quality of impact rather than the distance numbers.
- When you know the specs of the club, then and only then do you start with things like clubhead CG and flex profile, and only then do you worry about the sort of optimization that a LM can help with. But it is still very OK to keep the impact tape; it won't have a significant effect on the LM numbers. And the impact tape is the best way to tell whether to drop a data point. Think about it: an on-center hit with a club that fits the golfer is not one you want to reject as an outlier -- even if the LM numbers were totally different. The fact that such a shot can exist tells you something valuable.

Hope this helps,

DaveT