How do I make a NP chart in Minitab?

Steps to plot a NP chart in Minitab:

1. Click Stat → Control Charts → Attributes Charts → NP.
2. A new window named “NP Chart” appears.
3. Select “Fail” as the “Variables.”
4. Select “N” as the “Subgroup Sizes.”
5. Click the button “NP ChartOptions” to open a window named “NP Chart Options”.
6. Click the tab “Tests.”

How do you read a NP chart?

Interpret the key results for NP Chart

1. Step 1: Determine whether the number of defective items is in control. The NP chart plots the number of defective items (also called nonconforming units).
2. Step 2: Identify which points failed each test. Investigate any subgroups that fail the tests for special causes.

What is the difference between P chart and NP chart?

The main difference between P and NP charts is the vertical scale. P charts show the proportion of nonconforming units on the y-axis. NP charts show the whole number of nonconforming units on the y-axis.

What is NP control chart?

An NP chart is a data analysis technique for determining if a measurement process has gone out of statistical control. It is sensitive to changes in the number of defective items in the measurement process. The “NP” in NP charts stands for the np (the mean number of successes) of a binomial distribution.

How are NP and P charts used in MINITAB?

With a P chart, the center line is straight. With an NP chart, the center line varies with subgroup size changes. Values for Poisson data are often counts of defects or events. Poisson data are often used to model an occurrence rate, such as defects per unit. You can use either the U chart or the C chart to plot your nonconforming units.

How to calculate subgroup size in np chart?

In Subgroup sizes, enter 500. Click NP Chart Options. On the Tests tab, select 1 point > K standard deviations from center line (Test 1) and K points in a row on same side of center line (Test 2). If you are not sure which tests apply in your specific situation, use Tests 1 and 2 when you first establish the control limits based on your data.

What’s the difference between U and C in MINITAB?

You can use either the U chart or the C chart to plot your nonconforming units. The main difference between U and C charts is the vertical scale. U charts show the number of nonconformities per single unit on the y-axis. C charts show the number of nonconformities per sample, which can include more than one unit on the y-axis.

How to create an attribute control chart in MINITAB?

Minitab offers several attribute control charts that plot nonconformities (defects) or nonconforming units (defectives). Select your attribute control chart based on whether your data follow a binomial or a Poisson distribution. Values for binomial data are classified into one of two categories such as pass/fail or go/no-go.