Calculating Your Percent Error Index (PEI)

One of the topics that came up in class this week is Percent Error Index or PEI. The term was made popular by short game guru Dave Pelz in his first book in a four-book series, Dave Pelz’s Short Game Bible.

So what is PEI? It’s a percentage used to evaluate a player’s performance with a given club on a certain shot. After so many shots, an average can be calculated with the result being an accurate measure of a player’s skill with that club.

The way to calculate PEI is quite simple. It’s just the distance from the original lie to the hole or other target being aimed at divided by the shot’s finishing distance from that hole or other target.

For example, if a player is 100 yards from his target, and his shot lands seven yards from the hole, his percent error is 7/100 or 7%. This should be done for all the shots you hit with all the clubs in your bag (including your putter) to calculate a PEI for each club. PGA Professional Ed Ekis told us it would take us at least year of playing regularly and analyzing every shot for us to accurately determine our PEIs, and that’s not surprising when you realize how much work is involved. But once you know your PEIs, you can start playing shots to the yardages from which you are the strongest. Now you know your strengths and your weaknesses. A few years ago, Pelz wrote a great article on PEI for golf.com:

Master Awkward-Distance Pitch Shots
By Dave Pelz
golf.com

What is the “worst shot” in golf? It’s the 40-yard wedge, and I have the evidence to prove it.

Let’s start with a definition. By “worst shot,” I mean the one consistently executed with the least amount of success or accuracy. In my research over the years, I have measured the “error” for every shot in golf, with error being the distance the ball finishes from the pin divided by the shot’s original length. That means if a golfer hits a 9-iron from 100 yards and it finishes 20 feet (almost seven yards) from the hole, the Percent Error (PE) for that shot is about 7 percent. Hit 40 9-irons, average the PEs, and you come up with a Percent Error Index (PEI) for that shot and that player.

I’ve measured the PEIs of pros and amateurs on every kind of shot, from drives to putts. For drives and fairway woods, most pros average about 7 percent error; for irons, about the same; for wedges, about 15 percent; and for putting, 5 to 10 percent. Amateurs’ PEIs extend over a much wider range, of course, depending on their skill level. I’ve also measured many of the specialty short-game shots — greenside sand, chips, pitches, and so on. (Measuring the PEIs of all your shots is a wonderful way to determine your strong and weak areas and chart your progress. I highly recommend it.)

Based on more than 25 years of PEI data, I can state without reservation that the “worst” shot in golf for the amateur is the short wedge shot from about 40 yards, when you’re too far away to chip and too close for a full swing with even the most lofted wedge.I’ve measured the PEIs of pros and amateurs on every kind of shot, from drives to putts. For drives and fairway woods, most pros average about 7 percent error; for irons, about the same; for wedges, about 15 percent; and for putting, 5 to 10 percent. Amateurs’ PEIs extend over a much wider range, of course, depending on their skill level. I’ve also measured many of the specialty short-game shots — greenside sand, chips, pitches, and so on. (Measuring the PEIs of all your shots is a wonderful way to determine your strong and weak areas and chart your progress. I highly recommend it.)

The numbers are staggering. Before I show you how bad, look at some other poor results. A bad long putt may finish five or 10 feet long or short, but when starting 50 feet from the hole, that’s only a 10 or 20 percent error. Off the tee, even a bad drive is closer to your target (usually the center of the fairway, 200-plus yards off the tee) after you hit it than when you started (about the worst you can do on a drive is a 100 percent error, which is a whiff, and nobody averages that kind of error).

But on the 40-yard wedge shot, the error often ranges between 90 and 125 percent. And that’s from 90 percent short to 125 percent long.

Here’s how errors that bad can occur. When faced with the 40-yard wedge shot, one of two things usually happens. Either you “chunk” it — contacting the ground behind the ball and hitting it fat — or, as a result of repeated chunks, you overcompensate, hit the ball thin, and skull it. The fat shot travels only a few (three to four) yards, which equates to a 90 percent error short (it’s moved only 10 percent of the distance to the hole). The skulled shot flies 80 to 100 yards, or as much as 125 percent long, finishing 50 or 60 yards from the hole — farther away than before you hit the shot.

What causes this horrendous performance? It starts with seeing bad results — a few chunks followed by a few skulled shots — which leads to the expectation of bad results (having faced this shot before and hit it badly, you expect to hit it badly again), which produces fear. And once fear enters the equation, the worst swings and shots result.Admittedly, those are the extremes, but on average no other shot comes close to matching the errors I see in 40-yard wedge shots, which is why it’s the worst shot in golf. The average PEIs for the 40-yard wedge, measured over at least 40 shots, are pretty bad for all groups. Pros average about 15 percent error, 10-handicappers about 25 percent error, and 25-handicappers an incredible 50 percent error (where the ball finishes either halfway to the hole or halfway past).

Admittedly, those are the extremes, but on average no other shot comes close to matching the errors I see in 40-yard wedge shots, which is why it’s the worst shot in golf. The average PEIs for the 40-yard wedge, measured over at least 40 shots, are pretty bad for all groups. Pros average about 15 percent error, 10-handicappers about 25 percent error, and 25-handicappers an incredible 50 percent error (where the ball finishes either halfway to the hole or halfway past).

What causes this horrendous performance? It starts with seeing bad results — a few chunks followed by a few skulled shots — which leads to the expectation of bad results (having faced this shot before and hit it badly, you expect to hit it badly again), which produces fear. And once fear enters the equation, the worst swings and shots result.

And why do golfers chunk and skull their 40-yard wedges so frequently? Poor technique, caused principally by bad ball position.

Next month, I’ll show you three ways to hit the 40-yard wedge, as well as explain which one is best for you.

But since you may have to hit this scary little shot between now and next month, here’s a hint to help you hit it better: Move the ball back into the middle of your stance. This is what a “fat” 40-yard shot looks like… If the ball begins forward in the stance, the swing has to flatten out to reach it, so the club hits the ground first. After a few of these, expect to hit a “skull” over the green.