Exam 7: Statistical Process Control

A retail store manager is trying to improve and control the rate at which cashiers sign customers up for store credit cards. After posting a p-chart of the store's credit card sign-ups the manager takes new samples of size 50 three weeks later. He finds that each sample of 50 contained 5 credit card signups on average. Find p-bar and 99.73% control limits.

If $\overline { \bar { X } }$ = 23 ounces, ? = 0.4 ounces, and n = 16, the ±3? control limits will be

Plots of sample ranges indicate that the most recent value is below the lower control limit. What course of action would you recommend?

What does it mean for a process to be "capable"?

A process range chart illustrates the amount of variation within the samples.

The number of late insurance claim payouts per 100 should be measured with a

Assignable variation

The probability of rejecting a good lot is known as consumer's risk.

Pierre's Motorized Pirogues and Mudboats is setting up an acceptance sampling plan for the special air cleaners he manufactures for his boats. His specifications, and the resulting plan, are shown on the POM for Windows output below. Pierre is a bit confused. He mistakenly thinks that acceptance sampling will reject all bad lots and accept all good lots. Explain why this will not happen.

A Cpk index greater than __________ is a capable process, one that generates fewer than 2.7 defects per 1000 at the ±3σ level.

Define consumer's risk. How does it relate to the errors of hypothesis testing? What is the symbol for its value?

The steeper an OC curve, the better it discriminates between good and bad lots.

For an x-bar chart where the standard deviation is known, the Upper Control Limit

Mean charts and range charts complement one another, one detecting shifts in process average, the other detecting shifts in process dispersion.

An operating characteristics curve shows

Acceptance sampling

A nationwide parcel delivery service keeps track of the number of late deliveries (more than 30 minutes past the time promised to clients) per day. They plan on using a control chart to plot their results. Which type of control chart(s) would you recommend?

Some degree of variability is present in almost all processes.

If a process has only natural variations, __________ percent of the time the sample averages will fall inside the (or ) control limits.

Ten samples of a process measuring the number of returns per 100 receipts were taken for a local retail store. The number of returns were 10, 9, 11, 7, 3, 12, 8, 4, 6, 11. Find the standard deviation of the sampling distribution. (Hint- Use p-bar formula)