# Subgroup Size in Minitab for Capability Study

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#### Carmine

When filing the blank Subgroup size in minitab, I have to write or a costant or a ID Colomun. If i give a costant it means that the Subgroup is costant if i give a coloumn for example a clolumn tha contains date of production of some units it means that the Subgroup size can vary. Is that right?

I am saying that because I have to assess a capability study on many units produces in different days and in each day a different number of units had been produced.

So in assessing a capabability study the subgroup size can vary, am I right?

#### Jim Wynne

Staff member
Re: Subgroup Size in Minitab when assesing Capability Study

When filing the blank Subgroup size in minitab, I have to write or a costant or a ID Colomun. If i give a costant it means that the Subgroup is costant if i give a coloumn for example a clolumn tha contains date of production of some units it means that the Subgroup size can vary. Is that right?

I am saying that because I have to assess a capability study on many units produces in different days and in each day a different number of units had been produced.

So in assessing a capabability study the subgroup size can vary, am I right?
In most cases, subgroup size and frequency of sampling should remain constant regardless of the number of units produced. Are you doing rational subgrouping? Have you verified that your process is statistically stable?

C

#### Carmine

Re: Subgroup Size in Minitab when assesing Capability Study

This is a launch of a new product so one day we pruduce 15 unites another day 20 depends on what the customer want.

#### Jim Wynne

Staff member
Re: Subgroup Size in Minitab when assesing Capability Study

This is a launch of a new product so one day we pruduce 15 unites another day 20 depends on what the customer want.
What's the product? What are you measuring?

#### Miner

##### Forum Moderator
Staff member
When filing the blank Subgroup size in minitab, I have to write or a costant or a ID Colomun. If i give a costant it means that the Subgroup is costant if i give a coloumn for example a clolumn tha contains date of production of some units it means that the Subgroup size can vary. Is that right?

I am saying that because I have to assess a capability study on many units produces in different days and in each day a different number of units had been produced.

So in assessing a capabability study the subgroup size can vary, am I right?
From the technical perspective, Minitab will allow you to enter a column containing a subgroup identifier (such as a date) into the subgroup size field and will calculate the appropriate within subgroup variation.

However, the ability to do something does not mean that you should do that. This is what Jim is getting at through his questions.

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