statistical process

Question 1

types of variations

Answer 1

• assignable variations: traced to specific reasons , should be eliminated
• natural/random variations: inherent to the process, form a pattern, process in control when only natural variations

Question 2

type 1 and 2 error

Answer 2

type 2 error: assume the process is okay when its not
type 1 error: assume the process is not okay when it is

Question 3

How to find if a process is in control

Answer 3

use statistical info, take small samples : less costly, easier to see trends

Question 4

charts and what they control

Answer 4

x-bar: control the value
r-chart : controls the dispersion

Question 5

method for x bar and r charts

Answer 5

identify sample size = n
in each sample compute: x bar : mean
R : range

compute means of sample: x double bar: mean of x bar
r-bar : mean of r

Question 6

Take corrective action when

Answer 6

-one points falls outside the control limits
- seven points in a row on one side of center line
- a run of seven points in a row going up or going down
- two points in a row very close to a limit

Question 7

if binary variable

Answer 7

use p-chart:
- controls the percentage of defective items
and x-chart

Question 8

method p-chart

Answer 8

identify sample size: n
in each sample compute: p: fraction of defective items
compute means of sample: p-bar
computer standard deviation
compute control limits

Question 9

what happens when z increases

Answer 9

the probability of type 1 error decreases
the probability of type 2 increases