Reference
Control chart scheme
Plotting the measured data will reveal
process irregularities when points fall
outside the bounds or are clustered on
one side of the centerline.
●Control chart
A “control chart” expresses the status of work processes using a line
chart.
For example, the chart here shows irregular points based on the following
criteria:
• Any points outside the control bounds, either high or low
• If there are six or more points in a row above or below the centerline, the
sixth point and beyond.
Based on these criteria, there are three points judged to be irregular in the
example chart.
Irregularity out of bound
Upper
control bound
Upper limit
Centerline
Median data value
Lower
control bound
Lower limit
Irregularity biased to one side of median
●Histogram
A “histogram” is a method for representing the number of elements in
each group as a bar graph, dividing totaled data into some number of
groups.
A histogram can reveal an overall picture of the data, the central position,
range of variation, etc.
For example, this chart shows the results of a survey of cellular phone
owners in a certain city broken down by age group, revealing that cellular
phones are most common among people aged 21-30, followed by people
aged 10-20, then 31-40, and that they were least common among people
aged 51 and over.
Number of people
Number of cellular phone
owners (City X)
50
40
30
20
10
∼
∼
∼
29
∼
10
or
less
10
21
31
41
20
30
40
50
51 Age bracket
or
more