Block 5 - lecture 2 Flashcards
in a p chart how far away are control limits from the central value?
3 standard deviations
how to make a p chart more effective?
being visible to operating and quality personnel
how does a nonconforming unit effect the subgroup?
surrounding units are more likely to be nonconforming due to shared assignable cause, so more likely to show up in the subgroup
when aren’t p charts with a constant subgroup size possible?
100 percent inspection, as this changes
how does a changing subgroup size effect the p chart?
central line and control limits need to be recalculated for each sub group
why isn’t production always consistent?
- machines break
- different length shifts
- breaks
- worker morale
how to speed up p chart limit calculations?
simplify the part of the equation that doesn’t change
what happens to the p subscript 0 value over time? what does this mean?
improves, so should be recalculated periodically
what does lower case phi represent?
population proportion nonconforming (same as p subscript 0)
when are limits for p charts calculated?
end of each subgroup (eg. end of the day)
how to minimise the effect of a variable subgroup size on a p chart?
- control limits for average subgroup size
- control limits for different subgroup sizes
control limits for average subgroup size?
an average subgroup is calculated and shown for all subgroups (except when p is close and the actual limits are calculated)
how does a larger subgroup size effect the limits?
the limits are closer
when can you assume that proportion nonconforming is within limits when using average subgroup size in a p chart?
when the point is inside the limits for average subgroup size and the subgroup size is smaller than average
when can you assume that proportion nonconforming is outside limits when using average subgroup size in a p chart?
when the point is outside the limits for average subgroup size and the subgroup size is larger than average
