38 Questions
What type of data is often used in attribute control charts?
Discrete data
Which of the following is NOT a type of attribute control chart based on the Binomial Distribution?
u chart
What is the main purpose of using a p chart?
To monitor the proportion of defective items
Which of the following attribute control charts is based on the Poisson Distribution?
u chart and c chart
What type of distribution is used to create the np chart?
Binomial Distribution
What is the primary use of attribute control charts?
To evaluate variation in a process
Which of the following is a characteristic of attribute control charts?
They are used with discrete or count data
How many main types of attribute control charts are there?
Two
What is the primary concern of the supervisor at the small hospital in the illustrative example?
Keeping the number of errors in the medical records in control
What type of chart is used to monitor the proportion of defective items produced by a process?
Laney P' chart
What is the effect of overdispersion on a traditional P chart?
It shows an increased number of points outside the control limits
What is the purpose of using a Laney P' chart in the radiology department example?
To monitor the proportion of patients requiring a retest due to imaging errors
What is the average subgroup size in the illustrative example?
More than 2,500
What is the effect of underdispersion on a traditional P chart?
It shows too few points outside the control limits
What is the name of the chart used in the illustrative example?
P chart diagnostic
What is the purpose of the P chart diagnostic test in the illustrative example?
To test for overdispersion
What is the purpose of using a U Chart in quality control?
To monitor the number of defects per unit
What is the formula for the probability of x occurrences in a specified time or space?
𝑃(𝑋 = 𝑥) = 𝑒^𝜆 * 𝜆^𝑥 / 𝑥!
What is the purpose of using Tests 1 and 2 in establishing control limits?
To detect instabilities in a process
What is the range of the variable X in the probability formula?
X can equal any nonnegative integer
What is the purpose of using an NP Chart?
To monitor process stability over time
What is the significance of 𝜆 in the probability formula?
The average number of occurrences over a specified time or space
What type of control chart is used to monitor the number of defective items that can be classified into two categories?
NP chart
What kind of data would require the use of a Laney P' chart?
Data with high average and overdispersion
What is the primary purpose of using a control chart?
To monitor process stability over time
What is the benefit of using an NP chart in a delivery service?
To monitor the number of delivery vehicles that are out of service
What is an advantage of using a Laney P' chart over a traditional P chart?
It is more suitable for data with overdispersion
What is the purpose of creating an NP chart in the illustrative example?
To monitor the number of light bulbs that do not light
In which menu can you find the option to create a Laney P' chart?
Stat > Control Charts > Attributes Charts > Laney P'
How many light bulbs are tested each hour in the illustrative example?
500
What is the formula for the average number of nonconformities per inspection unit?
x / n
What is the distribution of the variable x in the U chart?
Poisson distribution
What is the formula for the variance of the average number of nonconformities per inspection unit (u)?
λ / n
What is the purpose of the U chart in the illustrative example?
To monitor the average number of defects per set of pages
What is the input variable in the U chart for the illustrative example?
Errors
What is the subgroup size in the U chart for the illustrative example?
Number of Pages
What is the parameter of the Poisson distribution in the U chart?
λ
What is the formula for the mean of the average number of nonconformities per inspection unit (u)?
λ
Study Notes
STATISTICAL PROCESS CONTROL
- Statistical process control is used to evaluate variation in a process where the measurement is an attribute (i.e., discrete or count data).
ATTRIBUTE CONTROL CHARTS
- Attribute control charts are used to monitor the proportion of defective items or the number of defects per unit.
- There are two main types of attribute control charts based on:
- Binomial Distribution: p chart and np chart
- Poisson Distribution: u chart and c chart
P CHART
- A p chart is used to monitor the proportion of defective items where each item can be classified into one of two categories (e.g., pass or fail).
- It is used to monitor process stability over time and identify instabilities.
LANEY P' CHART
- A Laney P' chart is used to monitor the proportion of defective items and adjust for overdispersion or underdispersion in the data.
- It is used when the data exhibit overdispersion or underdispersion, causing a traditional P chart to show an increased number of points outside the control limits or too few points outside the control limits.
NP CHART
- An NP chart is used to monitor the number of defective items where each item can be classified into one of two categories (e.g., pass or fail).
- It is used to monitor process stability over time and identify instabilities.
U CHART
- A U chart is used to monitor the number of defects per unit, where each item can have multiple defects.
- It is used to monitor process stability over time and identify instabilities.
- The probability formula for a U chart is based on the Poisson distribution: 𝑒 −λ λ 𝑥 / 𝑥!
- The average number of nonconformities per inspection unit is 𝑢 = 𝑥 / 𝑛, where 𝑥 is the total number of nonconformities and 𝑛 is the number of inspection units.
This quiz covers statistical process control, attribute control charts, and capability analysis. It is a part of the STAT 20223 course.
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