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Standard Deviation, Hey nerds


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Cannon

I have been working on adding standard deviation to the ratings data at CPW.  

Question: What is an acceptable sample size?

I've seen stuff as low as 10.  I've seen weirdly specific numbers like 26.  It seems like everyone agrees 100 is enough.  

Anyone who is statistics savvy (is this math? chemistry?) have any input?  

What is an acceptable sample size?

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richcottrell

Great question.... default answer:

42446401-A510-4442-B240-7DE2646FA70B.jpeg

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Cannon
16 minutes ago, richcottrell said:

Great question.... default answer:

42446401-A510-4442-B240-7DE2646FA70B.jpeg

C’mon Rich!  What’s safe? What’s responsible?

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richcottrell

But seriously, you are the only person with real numbers... I got a “D” freshman year at Penn State in basic college algebra so numbers still puzzle me!

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Tom Flesher

Honestly, I think it’s most responsible to report the mean, the SD and the number of observations, but that would require updating somewhat regularly. If you wanted to really get crazy you could report a 90% confidence interval (excel can do this really easily if you’re interested). Off the top of my head I can’t recall a test for whether a standard deviation is statistically reliable.

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Climber028

I would be more interested in the variance than the standard deviation. As for sample size ironically the amount you should have depends on the deviation, obviously the more the better but I would feel good with 30-50 when speaking about grippers. 

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Cannon
34 minutes ago, Climber028 said:

I would be more interested in the variance than the standard deviation. As for sample size ironically the amount you should have depends on the deviation, obviously the more the better but I would feel good with 30-50 when speaking about grippers. 

What do you mean by variance. Min and max are already published. 

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Climber028
11 minutes ago, Cannon said:

What do you mean by variance. Min and max are already published. 

You might be thinking of range, which is just the difference between maximum and minimum. Variance is a different value related to standard deviation. Excel calculates it automatically so I won't bore people with the details but in plain language it's a measure of how spread out a set of data is. That's what I would want to know when looking at ratings data, but I'm weird so it might not be what most people need or want.

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Cannon
13 minutes ago, Climber028 said:

You might be thinking of range, which is just the difference between maximum and minimum. Variance is a different value related to standard deviation. Excel calculates it automatically so I won't bore people with the details but in plain language it's a measure of how spread out a set of data is. That's what I would want to know when looking at ratings data, but I'm weird so it might not be what most people need or want.

Okay i’ll check that out. :)

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richcottrell

You guys have gone over my head, but I thank you for crunching numbers for us... now I will go back to my remedial mathamatical studies:

5D59592E-636C-4FD4-A434-BF9603E3E1B7.jpeg

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Cannon
1 hour ago, richcottrell said:

You guys have gone over my head, but I thank you for crunching numbers for us... now I will go back to my remedial mathamatical studies:

 

This is all a little over my head too.  I don't have any experience using these types of calculations, but can make Excel do it.  But even though I can, i'm stopping to wonder if I should.  :)

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Climber028

It seems like most people are satisfied with the data you provide currently. Tho it's not much extra work to throw in a few extra columns on excel so I can't see a reason not to do it. If that's too cluttered you can even separate it by having your normal ratings data then a secondary section for "advanced analysis" or whatever. Or even sell people the raw dataset.

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Graph what you have and add links to the pictures. Max/min/average is enough for most people, the rest can look at the bell curve.

The number of people who will fully understand and appreciate the statistical definitions is very small (I'm not one of them.)

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WestSlope
1 minute ago, wobbler said:

Graph what you have and add links to the pictures. Max/min/average is enough for most people, the rest can look at the bell curve.

The number of people who will fully understand and appreciate the statistical definitions is very small (I'm not one of them.)

My thought as well. Link a scatter plot or graph an let people interpret the data as they chose.

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Tom Flesher
3 hours ago, wobbler said:

Graph what you have and add links to the pictures. Max/min/average is enough for most people, the rest can look at the bell curve.

The number of people who will fully understand and appreciate the statistical definitions is very small (I'm not one of them.)

Not a bad idea, considering how easily you can chart this stuff in Excel.

If you’re interested in something that looks a bit more professional I could toss up a chart for you in R. It’d take a hot second.

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Gary Gray
6 hours ago, Climber028 said:

It seems like most people are satisfied with the data you provide currently. Tho it's not much extra work to throw in a few extra columns on excel so I can't see a reason not to do it. If that's too cluttered you can even separate it by having your normal ratings data then a secondary section for "advanced analysis" or whatever. Or even sell people the raw dataset.

I personally like what what Cannon Powerworks is doing now and I am very happy that they are taking the time to do it.   No need to change anything.

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Adam Juncker

Standard Deviation would not be that helpful, its just average amount of deviation from the mean.  Smaller numbers generally mean a more consistent process, with a SD of 0 being no variation.  So.... on grippers that you don't have a large sample size (GHP 10 for example), you would likely see a higher SD and people might be all like "Whoa, them GHP's got some variation" when they really don't, we just don't have enough data.  

With the information you already provide (Average, Min, Max, and the sample size), those of us that really care can figure out the info we want.  Perhaps you could publish the "mode" for each gripper, that would tell us which rating you get the most.  It can also help predict a shift in ratings.  

It might be interesting to break out the ratings by the year too.  Everybody knows that grippers are way harder now than they were 5-10 years ago 😝

 

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Cannon

So far I was only taking the time for sample sizes of 100+. Which, is only a handful of the most popular grippers. 

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Cannon

I appreciate the feedback. Since this is extra work, I likely won’t chase it too hard.  

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Cannon
7 hours ago, Tom Flesher said:

Not a bad idea, considering how easily you can chart this stuff in Excel.

If you’re interested in something that looks a bit more professional I could toss up a chart for you in R. It’d take a hot second.

What is R?

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Adam Juncker

If your ratings data is already in excel, and your ratings for each gripper are all in one row or column, you can just use the formula to calculate it. 

=stdev.s(highlight your row/column).

This will give you the standard deviation of the sample and it calculates it based on the sample size that you provide.  So if you have 200 ratings of CoC3's, then it will calculate it based on the sample size.  

something like this....  All the gripper ratings here are randomly generated numbers... just for demonstration:  

Gripper Ratings Data Coc 3 GHP 7              
157 146              
150 147              
153 152              
146 149              
150 143              
152 142              
138 154              
164 151              
150 144              
146 146              
166 142              
153 142              
163 150              
143 152              
144                
143                
160                
154                
Min 138 142   formula for min is "=min(B2:B19)"    
Max 166 154   Formula for max is "=max(B2:B19)"    
Mean 151.8 147.1   Formula for mean is "=average(B2:B19)"    
Sample size 18 14   Formula for sample size is "=count("B2:B19")  
Standard Dev. 7.90 4.20  

Formula for standard deviation is "=stdev.s(B2:B19)"

               
     
Edited by Adam Juncker
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Cannon

I am using array formulas because everything is in a huge list by order # and the formula has to check multiple points of data from different columns to pull out min/max, etc. 

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