Block 5 - lecture 1

Question 1

What does ‘attribute’ refer to?

Answer 1

when a quality characteristic comforms or doesn’t conform to specifications (pass/fail)

Question 2

When are attributes used?

Answer 2

measurements are:

• not possible
• time consuming
• costly
• not needed

Question 3

When aren’t measurements possible?

Answer 3

• visibly inspected eg. colour, missing parts, damage

Question 4

Example of quantitative measures being too time consuming?

Answer 4

vernier vs go-no-go gauge

Question 5

nonconformity?

Answer 5

part doesn’t meet specification

Question 6

defect?

Answer 6

part doesn’t meet usage requirement

Question 7

nonconforming unit?

Answer 7

an example of the product or service that has a nonconformity

Question 8

limitations of control charts for variables?

Answer 8

• don’t work when the quality characteristics are attributes

- an Xbar and R chart for each characteristic could be expensive

Question 9

types of attribute charts for nonconformity?

Answer 9

• p chart

- np chart

Question 10

p charts?

Answer 10

a Proportion chart showing the proportion nonconforming in the subgroup (% or 0.)

Question 11

np charts?

Answer 11

Number of nonconforming

Question 12

types of attribute charts for nonconformities?

Answer 12

• c chart

- u chart

Question 13

c chart?

Answer 13

count of nonconformities on single units

Question 14

downside of p charts?

Answer 14

• typically low proportion nonconforming means large subgroups are needed
• less sensitive to variation than Xbar and R

Question 15

possible uses of a p chart?

Answer 15

• control a characteristic (like with Xbar and R), a group of characteristics or the entire product
• determine average quality level
• show changes in the average
• show improvements / effectiveness of ideas
• measure performance of operators and management
• determine acceptance before shipment to customer

Question 16

subgroup sizes for np and p?

Answer 16

np chart - constant

p chart - variable or constant

Question 17

process for p chart construction?

Answer 17

1. select quality characteristic (eg. single characteristic, part or product)
2. select subgroup size (>50) use equation with Z from confidence limit
3. collect data (>25) and calculate proportion nonconforming
4. calculate trial central line and control limits
5. discard data with assignable cause and calculate revised central line and control limits