Finding standard deviation of ranges in Minitab

[Jim Thomson]

I have recently been assigned the task of calculating a variety of statistics for our top 15 products. The one statistic that has me baffled is the sigma of the ranges. I can't seem to find it in Minitab. Is there a way to do this in Minitab? Thanks.

Jim Thomson

[Miner]

Originally Posted by Jim Thomson

I have recently been assigned the task of calculating a variety of statistics for our top 15 products. The one statistic that has me baffled is the sigma of the ranges. I can't seem to find it in Minitab. Is there a way to do this in Minitab? Thanks.

Jim Thomson

How do you intend to use this information?

You can brute force this information by putting each value of the subgroup in a separate column. Use the Calc by Rows function to calculate the Range and place the results in a new column. Then do statistics on that column to obtain the sigma.

However, I cannot understand why you would want this information. The Range is influenced by the subgroup size. This is why you have to use different A2, D4, d2, etc. constants based on subgroup size to calculate control limits.

[Darius]

Originally Posted by Jim Thomson

The one statistic that has me baffled is the sigma of the ranges.

Maybe I don't understand but..

Setting MINITAB Options

Methods and Standard Values

Statisticians sometimes disagree about the best methods for estimating certain parameters. Similarly, acceptable standard values (like alpha levels) may vary from person to person or company to company. Options allow you to choose your preferred test methods and parameters.

Problem: You prefer to use the average of subgroup ranges to estimate the standard deviation in n X-R chart.

Solution: Change the estimation Options setting.

and welcome to the cove.

[Jim Thomson]

This is a customer driven requirement. I asked the same question as I have never seen this metric before.

I will probably use the "brute force" method and grind through the thousands of numbers We have a great deal of data but it is not readily available.

Thanks for the help in this.

Jim Thomson

Originally Posted by Miner

How do you intend to use this information?

You can brute force this information by putting each value of the subgroup in a separate column. Use the Calc by Rows function to calculate the Range and place the results in a new column. Then do statistics on that column to obtain the sigma.

However, I cannot understand why you would want this information. The Range is influenced by the subgroup size. This is why you have to use different A2, D4, d2, etc. constants based on subgroup size to calculate control limits.

[Statistical Steven]

Originally Posted by Jim Thomson

This is a customer driven requirement. I asked the same question as I have never seen this metric before.

I will probably use the "brute force" method and grind through the thousands of numbers We have a great deal of data but it is not readily available.

Thanks for the help in this.

Jim Thomson

General question here....if the customer asks for an invalid statistical analysis, do you do it just because they ask for it?

Can you ask the customer what does sigma of the range mean? Sounds like you are taking the variance of variances.

[David Hartman]

Originally Posted by Jim Thomson

I have recently been assigned the task of calculating a variety of statistics for our top 15 products. The one statistic that has me baffled is the sigma of the ranges. I can't seem to find it in Minitab. Is there a way to do this in Minitab? Thanks.

Jim Thomson

You might want to give your customer a call and ask their intent. Because as I read this they could be asking for "the sigma of ranges [or list of numbers, instead of the statistical meaning of the word "range"]. In other words, their intent may be as simple as asking for the sigma of your actual data. Then again, maybe not - but you will not know without asking.