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Monday, 26 March 2012

Playing with statistics part 5

Posted on 03:45 by Unknown

Although at the end of part 4 I mentioned I will talk about analysis of frequent tests like sRPE, HRV and other’s that are used for monitoring, I will not do that in this part. Maybe in part 6 because I am still ‘playing~struggling’with that one. What I want to talk today is data visualization.

A friend of mine and a fellow coach Carl Valle (check the interview with him here) is big into data visualization. There is a lot to be said regarding this and I myself saw the BIG differences when I visualized the data the right way. 

I remember in my high school when the professor of electronics said that in Power Plants they use analog dashboards versus digital, because humans respond and understand analog dashes more (“is it red?”) than digital (“is it above 36,785?”), besides it takes them less time to scan 20+ instruments in analog form, that in digital form. Imagine reading 20+ numbers or just watching 20+ analog indicators. And yes, they showed less decision making errors. At least according to my professor. 

Digital dashboard
Analog dashboard

The point of this is that I printed the table with the scores and guess what? No one understood.

The players would say WFT?   


Then, the scientist in me wanted to print them Z-score so the guys know where each of them stand regarding the team mean value. 


 
Or, even worse, I combined (in another test) z-score in test value with z-score in improvement so the guys can know their ranking within the group.

More players would say WTF and why am I below zero? Does that mean I bad?

Well, no one understood! Athletes are not scientists. Keep the Z-score and quadrant analysis for coaching staff and yourself. First of all, they don’t understand. Second, they want to see the improvement to be motivated. No one understand why their improvement is negative in Z-score. How do you think this is going to impact their motivation (“Mladen, why I am below zero in squat?”). To keep the long story short, if you want to present the data think about the observer and what does he takes out from the data. 

So, I decided to present the absolute scores (for example in relative bench press; please note that I had hard time explaining what is relative strength and how it is calculated as well, but less straining than explaining Z-score) both in level reached and improvement. Everybody is above zero, so it doesn’t screw with their motivation :)

Ahaaa.... now I understand - I am stronger that Athlete number 19... 

 
I have also created basic Medal Ceremony, where three best players are awarder with medals. On paper of course. 


 
What I also learned in the last couple of days between writing these blog entries is how much data visualization can help coach to make better decisions. At the moment my professional interest is individualization of training in team settings using monitoring of workloads, training reactions and fatigue and adaptation of the athletes. So, I collected all the testing data in one Excel sheet and I wanted to create player evaluation based on the test scores and test improvement so I can make training decisions for each more easily.  

I decided to use spider graph to visualize the Z-score. Again, the Z-score tells me how much an athlete is away from the team average. What does this mean is that I can check (using the other monitoring data) whether the general training is enough for certain athlete (if I take his reaction to training into account). In other words it helps me individualize training (although in team setting that is really hard) and it helps head coach to see player characteristics more easily.

Here are the three players for an example. 


 
You can see that the player have different qualities. What we can also do is to depict how did the player responded (improved) to a training program we did (again expressed in Z-score so we can compare it to the team average).

 
Please note that I showed only test with the re-test (4 re-test). What you can see on the right spider graph is that this athlete responded the most to endurance training and he was so-so in the strength improvement. What this can tell me is that he might need different strength training program. Maybe more. Maybe less if he is fatigued (this depends on the other indicators calculated by monitoring). 

IMHO, spider graphs of both test score and test improvement, together with Quadrant Analysis™ and monitoring data can tell you a lot about an athlete. Of course, if the test you are using are valid, reliable and sensitive. This can be also tested, but it is beyond this article. 

For the end here is the picture of the  Quadrant Analysis™ I use used for 30-15IFT analysis of the players.  

 
This is all for now folks. I will come back with some ideas how to analyze monitoring data based on individual variations and team variations. Stay tuned….
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Posted in analysis, energy system development, monitoring, Performance Analysis, planning, programming, RPE, RSA, soccer, statistics, team sports, Theory | No comments

Monday, 19 March 2012

Playing with statistics part 4

Posted on 16:19 by Unknown

In the last part I did analysis of the test using standard score. Now I am going to analyze re-test. Here are the test score for both test and re-test.



TEST

RE-TEST


January 14th, 2012.

February 25th, 2012.
Player

v30-15IFT
Z-Score

v30-15IFT
Z-Score
1

19,5
-0,89

20
-1,44
2

19
-1,57

20
-1,44
3

19,5
-0,89

20,5
-0,78
4

20,5
0,45

21
-0,11
5

19,5
-0,89

21,5
0,56
6

20
-0,22

21
-0,11
7

21
1,12

22
1,22
8

21,5
1,79

22
1,22
9

21
1,12

22,5
1,89
10

19,5
-0,89

20,5
-0,78
11

19,5
-0,89

21
-0,11
12

19,5
-0,89

20,5
-0,78
13

20,5
0,45

21
-0,11
14

20
-0,22

21,5
0,56
15

21,5
1,79

22,5
1,89
16

20
-0,22

20,5
-0,78
17

21
1,12

21
-0,11
18

20
-0,22

20,5
-0,78














Mean

20,17
0,00

21,08
0,00
SD

0,75
1,00

0,75
1,00







Min

19,00
-1,57

20,00
-1,44
Max

21,50
1,79

22,50
1,89

Here is the histogram of the two tests. 


Now, there are two methods to calculate change (or improvement) between test and re-test IMHO. One is absolute where one just does the (re-test)-(test) (e.g. 21km/h – 19.5km/h, which is 1.5km/h) or relative which is this difference divided by the test [(re-test)-(test)]/(test) and that could be expressed as percentage (e.g. (21km/h – 19.5 km/h)/19.5, which is 7.69%. Honestly I don’t know which one is better, so I will utilize both. In the next table there is absolute change and relative change and their z-scores. 


We see that the team improved for 4,58% on average (relative change) or for 0,92 km/h on average (absolute change). 

The next thing I did is to create correlation table between these 4 data sets (test, re-test, absolute change, relative change). 

r
Test
Re-test
Absolute
Relative
Test
1



Re-test
0,80
1


Absolute
-0,31
0,33
1

Relative
-0,37
0,27
0,997
1

At the moment I don’t know how to measure significance and/or Student T test to test hypothesis, so I will only use Pearson’s correlation coefficient. (Someone please correct me if the thing I just said is plain gibberish)  

As we can see test and re-test have strong correlation (0,8) as well as relative and absolute change (0,997). We can also see the negative correlation between test and relative and absolute change (-0,31 and -0,37) which basically means that someone with higher test result will tend to show lower change. This is  a common occurrence with almost all qualities – the more advanced you are the less (and harder) you improve over time. The correlation in this case is moderate (-0,37). 

Here is the scatter of test and relative scores with the trend line.  

 
What is also interesting to do is to calculate the Z-score of the changes, which I did in the table. Using this we can identify outliers – those who are non-responders and those who are maybe on some form of AAS. Kidding aside, this is a useful tool.


 

From the graph above we can see that athlete number 5 improved for 10,26% with Z-score of 2,33. In this example he should be red flagged. This doesn’t mean anything, but rather necessities for  more analysis. Maybe he did not push on the first test. Maybe there is an error in measurement. Maybe he took Ephedrine. Same with the guy number 17. He didn’t improve at all. He should be red flagged as well. Maybe he did not push in the re-test. Maybe he is non responder. Maybe the training was not enough for him (undertrained) or even too much (under-recovered), so he didn’t show any improvement. Basically, we don’t know thus he is a suspect for further analysis.

If you are more interested about responders and non-responder make sure to check this article and this one, and make sure to check mentioned papers within them (like Vollard et al., and  Timmons et al.).

Going back to my four quadrant analysis – here is how the data looks with these athletes:


 
To be honest I got this idea WHILE I was writing this blog posts. This is why I actually like writing and reflecting – I got more ideas or they somehow emerge along the way. Anyway, I think that this idea of quadrants is very interesting. I can red-flag players and I can create different workouts based on their trainability and level of the certain tested quality. We can also identify potential talents, or non-responders. This might be interesting (especially if it could be applied to skills as well, like on the ball skills and decision making in the game) to identify strengths~weaknesses of the players and put them at certain playing positions (if they are non-responders) or modify training to get them more fit for different positions suited to coach style of play. IMHO it is interesting tool. 

For example in the quadrant analysis above athletes 9  (higher initial score, higher responsiveness) and 1 (lower initial score, lower responsiveness) would probably demand different approach to training. It is beyond the scope of this article to go into how to utilize this quadrant analysis. It is also beyond my current knowledge as well – I am just starting to experiment with it. 

That is for now folks. In the next installment I will cover how to do analysis for more frequent tests like sRPE, HRV and others we use for monitoring (this deals with comparing players baseline and his variability to himself rather than team average and variability). Stay tuned…
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Posted in analysis, energy system development, monitoring, Performance Analysis, planning, programming, statistics, team sports, Theory | No comments
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