Friday, March 21, 2014

The Study - Differential versus Calibrational

When I was working in Austria, I was lucky enough to have an endless supply of fresh beginner golfers with no preconceived ideas of how the game should be played. This was a great chance for me to not only teach them golf, but do some research into how best to improve a skillSKILL set.

The goal for these golfers was simple – I had to get them around a golf course in a defined number of shots so that they could earn their ‘Platzreiferkurs’ – a certificate which allowed them to play on the course. So, I decided to focus on the main skills which a beginner should focus on. My first study involved improving the player’s ability to hit the middle of the face; a vital skill for quality play.

Beginner golfers


Each participant was given a one hour lesson where they were shown grip, stance, posture and ball position in basic. Much of this instruction was a simple ‘copy me’ approach, where I asked questions to the students to direct their awareness, such as “where is my ball in relation to my feet”?  

After they had a basic idea of the swing, each participant was educated on the fact that, for optimal distance and control, the ball should be struck from the sweet spot, which equates (roughly) to the middle of the clubface. We then did a 20 ball test (PRE) to see how many times they could strike a spot the size of a 1 euro coin drawn on the centre of the face.

24 golfers were then split into 2 groups, with average abilities matched; Calibration (CAL) N=8, Differential (DIFF) N=8, and Combination (COMB) N=8.

The calibration group were asked to hit shots and try to hit the 1 Euro size circle as often as possible. The Differential group has a line drawn down the middle of the clubface and were asked to hit 5 shots from the toe side, followed by 5 shots from the heel side. The Combination group did a mixture of both practices, starting with the differential practice and finishing with calibration. Participants did this practice for 3 x 1 hour sessions during the week.

After the first hour, a second 20 ball test was conducted (POST). Then, at the end of the week a final 20 ball test was completed (FINAL). The test parameters were the same for all groups - Hit the centre of the face in a 1 euro size circle.

CALI group tried to hit this size spot over and over

DIFF group tried to hit 5 shots from the toe side, followed by 5 shots from the heel side


Below is a table showing the results of the study


So the calibration group improved by 10% after one hour (the most improved group after 1 hour), and by 16% after a week. Differential practice group improved the lowest amount after 1 hour (4%), but leapt ahead of the calibration group by the end of the week by improving 24%. The Combination group showed an improvement of 8% after one hour, and a massive 30% by the end of the week. They were almost hitting half of their shots flush, which is quite an achievement for a beginner.


All improved

The first point to note is that all golfers improved. This is obvious, and I would have been doing a very poor job if they hadn’t gone from complete beginner to ‘better golfer’ in the space of a week. Even over the course of an hour, every group improved. This is simply down to the nature of learning – people generally get better at things the more they practice them, especially as a beginner. But it is also an important point to note. Lots of people can claim that their method improves golfers, but is it the actual method which is working, or is it the fact that someone is simply practicing more.

There could also be elements of Hawthorne effect, or certainly Placebo effect being involved. For this reason, it would be good to compare the groups against a control group. For example, if the control group showed improvements above and beyond another group (or all of them), it could be concluded that, although there was an improvement, the intervention was actually more detrimental than no coaching at all. Unfortunately, collecting data on strike pattern without the control group being aware of what was going on was difficult, and so I decided to leave a control group out of it.

Short term versus long term - calibration

It is important to note that there was a difference between the short term improvements and long term improvements in performance. The calibration group was the most improved after one hour, but the least improved after a week. This can be very important information for both players and teachers. If you need short term success and maximum improvement in a short amount of time (likely intra-day), it would be best to try a calibration style of practice, where you simply hit balls with the aim of doing it correctly each time. As long as you are getting good quality feedback and are aware of the goal, it will be valuable practice.

I believe the reasons for the quicker rate of performance improvement are an improvement in confidence levels during the intervention, and neuromuscular priming. The Calibration group were seeking good shots, so they got to hit them more often. This builds a good feeling and gives the person a (false) sense that maximal learning is occurring. Also, as the player was trying to undertake one single task (hit the middle), they were sending the same unconfused signal to the brain and body. A less variable signal resulted in slightly better performance in the short term.

There is a dark side to this, which most people don’t understand about human psychology. If you perform too well, this increases EXPECTATIONS. I noticed that the majority of CAL group participants arrived the next day with the expectation to perform as good as they did the day before, and were more disappointed and frustrated when it didn’t happen immediately, which probably resulted in their lowered overall improvement at the end of the week.

This practice provided instant gratification, but not necessarily better results.

But the message here is, if you are looking to improve your ability to hit the middle of the face before a round of golf, try simply calibrating it during the pre-round session. For teachers, to get the most improvement in performance out of your students in one single session, a calibrational approach may work best for most.


This group was interesting as they showed the least amount of improvement during the first hour, but beat the CAL group by the end of the week. This is the funny thing with learning – what happens in the short term does not always translate in the long term. There is also a difference between LEARNING AND PERFORMANCE

The Differential group finished a close second by the end of the week. So why did they under-perform during the initial 1 hour testing? From observing the students, it was clear that by asking them to hit the toe or the heel of the club during their training, even if they got it correct, the result was poor. I think most people can’t see the end goal (even if it is explained to them very clearly beforehand), and so this group didn’t understand that they were actually getting better, even though they were hitting bad shots.

The difference was, they were INTENTIONALLY trying to hit poor shots as part of their intervention. If you do something intentionally and get quality feedback, there is so much more learning occurring than if you were to hit the same poor shot unintentionally and have no feedback. For example, a shank is devastating if you didn’t mean to do it (especially if you don’t even understand that you hit it with the hosel of the club). But, if you intended to do that, it is actually improving your ability to match reality and intention, which will aid you when it comes to hitting the middle of the face. So the DIFF group went into the first hour of testing with poorer confidence, as they had spent the previous hour hitting shanks and toe shots. 

Also, there is a good chance that the confused neuromuscular signals from alternating the goal (5 toes, 5 heels) combined with no calibration work held back their improvement.

But, it is still worth mentioning that they improved. One of my beliefs for why they improved so much during the week was because

1.       They saw that this style of practice can improve them
2.       They built subconscious tools for changing where they hit on the face
3.       They had lower expectations due to the difficulty of the task

Notes for the teacher – this is probably not the best method to use if you are looking to build the confidence of a player and to get them to come back to you if it is your first time together. The post intervention testing can eliminate a lot of those problems by showing the player that they have improved at the end of the session, but by that time, the player may be feeling frustrated. It is unfortunate, as, in the longer term, this actually shows a significant amount of improvement.

For players – don’t judge your learning by your results. Just because you are hitting poor shots doesn’t mean you are not learning. In fact, you may be learning more than if you were hitting good shots. Oh the paradox!

Combi group – most improved

This group showed the second biggest improvement after one hour, and the most improvement by the end of the week. It seems that the differential practice helped to build the players’ ability to change where they hit on the face, and the calibration afterwards allowed them to manifest those new skills. I also think the order in which the intervention was conducted (differential practice first followed by calibrational) played a major role in the testing. Players went into the testing with higher levels of confidence than the DIFF group. I wonder if they would have had the same success had the order been switched?

I assume the reason why the initial testing was slightly lower than the CAL group was due to this intervention having more variation within it, causing a confusion of the nervous system during learning. However, after consolidation of this learning over time, players now had both the tools to move the strike around the face, and the confidence of the calibration period they had undergone. This lead to the greatest improvement in performance over time – a good indication of actual learning occurring.

Notes for teachers and players – if you want the best amount of learning, mixing a bit of differential practice with calibration work is the best for the long run. It will not only allow you to do what you want to, but it will give you the tools you need to teach yourself.

Other notes

I believe that one of the main reasons for a greater improvement within the groups which included some DIFFERENTIALwork was that there was an improved level of concentration during training. I cannot prove this directly, but it would seem obvious that, if you’re changing the shot by adding variance, it forces you to go through the mental preparation phase. This phase can be skipped out in the calibration training. A good analogy is if I were to ask you the same maths question over and over, you would soon zone out and not be computing anything in your head as you give the same answer over and over. Your performance would be great (as you would be answering quickly and correctly each time. However, if I were to ask you a different question each time, you would have to go through the process of thinking and calculating – which would make performance go down (speed of answer and possibly correctness), but learning in the long term would improve.

Also, not all golfers improved the most with COMB. Some improved more with the CAL approach, so while it is good to find generalizations which fit the majority (and most of the golfers clearly fit into the trend), it is important to know that everyone is individual, and coaching should be tailored to the student. You get to realize this the more you are with a person. Coaching is a two way process, and is more of a trial and error situation. Staring with generalizations can get the majority to better answers faster, but the answer may be different for everyone. It is only through testing different things that you will come to better answers and find out more about yourself.

Counter intuitive

A lot of this is counter intuitive, and it happened to shape many of my beliefs I hold now. I think more research needs to be done, but it is clear to me from my studies and further lessons that people of all abilities seem to respond well to variance. A lot of literature on motor learning now talks about how everything should be highly specific and we should practice with perfection in mind, but this study clearly shows the opposite (to a certain extent). The players who practiced context specific (CALI) improved the least. Players who hardly had any specific practice (DIFF) even won out against them. But it was the combination of both which showed the most improvements (COMBI). But one thing is for sure, the idea that “perfect practice makes perfect” is not true and may even be harmful to maximising learning.

But I am a scientific mind, and so until further research is done on players of all levels, it is not definitive whether the results would carry forwards. However, Anecdotally, it is no surprise to me that some of the best players in the world can perform some funky trick shots which they may never use on the course. And Tiger Wood’s ability to shape the ball is impressive, as he demonstrates in clinics. And he practices it too – Hank Haney states in his book (The Big Miss) that Tiger practices the 9 ball flights (high low and mid trajectory of fade, draw and straight shots). This variable practice followed by undoubtedly hours and hours of calibrational work has not done too much harm for him.

I can attest personally that, since I have been practicing more variable and differentially, my game has come on leaps and bounds. I now never struggle to calibrate a good shot. If I feel I am hitting it from the toe one day, I can quickly identify and change that pattern – much quicker than I could when I was practicing hours and hours of Calibration. Also, this skill seems to transfer to whatever technique I use. I often practice with silly/poor swing styles (to see what my clients are feeling), yet can still manage to get it back on the middle of the face.

Take Home notes

If you are going out on the golf course on the day, trying to calibrate one thing may provide the best results for you. But do not confuse this with learning. You will get much better learning long term if you actually mix it up a bit, and the most learning will come from a combination of both.

So every practice session you have, try to pick something to improve and then find a way of adding variability before zoning in on what you want. This can be applied to movement style as well as impact skills (such as divot control, strike control or clubface control). For example, if you are trying to improve your weight shift, try half of your practice trying to over-do it, followed by underdoing it (or even complete reverse) and then finish by zoning in on what you want.

Variable and Differential practice techniques may actually cause some performance disruption in the short term. Try to avoid using them close to playing or close to competition. A good practice schedule will include these elements, but will have them further away from important performance times. When I teach better players, I usually get them to perform more variable work at least a week away from major tournaments, often more. But it will usually be on a sliding diminishing scale.

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