Two batches - Is the subgroup 4 or 2?

[AJ05231969]

There are two batches we are measuring for 15 days. We took measurement on the first batch twice a day - 5:00 am and 5:00 pm (4 measurements each time).

We did that for 7 days and on day 8, we measured the first batch only at 5:00 am.

We started to measure the 2nd batch at 5:00 pm on day 8 and then every day until day 15.

Is my subgroup 4 or 2?

Our results change considerably different based on sub group.

What do you think the subgroup should be (2 or 4 and why)?

 

[Jim Wynne]

Welcome to the Cove. You posted the same question in three different forums. This leads to confusion so I deleted the other two.
Please describe what you mean by "batch." Are these separate process streams?

 

[AJ05231969]

I would just say Item 1 and Item 2 instead of batch. Measured 4 times at 5am and 4 times at 5pm. Item 1 for first 7 days and morning of day 8. Item 2 from afternoon of day 8 until day 15

 

[Jim Wynne]

I would just say Item 1 and Item 2 instead of batch. Measured 4 times at 5am and 4 times at 5pm. Item 1 for first 7 days and morning of day 8. Item 2 from afternoon of day 8 until day 15

The question remains--what do you mean by "item?" Are they two different things in two different process streams?

 

[AJ05231969]

The question remains--what do you mean by "item?" Are they two different things in two different process streams?

.
They are in the same process stream came out of the same line.

 

[Bev D]

You have a subgroup sample size of 4. You have taken 2 subgroups per day except the day when you took only 1 subgroup. (item 1 = 15 subgroups and item 2 = 15 subgroups; if I understood your count correctly.)
the subgroups for item 1 are probably not independent of each other. I don't understand why you stopped measuring item 1 and started measuring item 2 on day 8?

We really need a LOT more information to properly help you.

 

[AJ05231969]

The question remains--what do you mean by "item?" Are they two different things in two different process streams?

It is the same product coming out of the same line.

 

[AJ05231969]

You have a subgroup sample size of 4. You have taken 2 subgroups per day except the day when you took only 1 subgroup. (item 1 = 15 subgroups and item 2 = 15 subgroups; if I understood your count correctly.)
the subgroups for item 1 are probably not independent of each other. I don't understand why you stopped measuring item 1 and started measuring item 2 on day 8?

We really need a LOT more information to properly help you.

I am trying to use the data to understand the stability of the process, process mean and process range. the measurements are the width of the part.

 

[Bev D]

What do you mean by stability? Do you mean "is the process in statistical control"? or do you mean that the material might degrade over time?
(Given that this is a width I would assume the former and not the latter)

When you say you measured the 'items' or 'batches' twice a day for 7 days and then once on the 8th day, does that mean:
* It took ~8 days to manufacture the parts and you took 4 pieces at each time point during the manufacturing process?
* You a large random sample of parts and you took 4 pieces out of that sample set twice a day and measured them?
* or some other time sequencing?
The answer to this timing question is critical as to what you can do with the data...