1. Other Variable Control Charts
Chapter Seven
Control Charts

2. Other chart options
What happens when there is an insufficient number of sample measurements to create x-bar and r charts?
What happens when only one sample is taken?
What other charting methods are available?
Control Charts

3. Available chart options
Individual and Moving-Range
Moving-Average and Moving-Range
All Individual Values
Median and Range charts
Run charts
Variable sub-group size
Pre-control charts
Control Charts

4. Individuals and Moving-Range
Used when measurements are single values or when the number of products produced is too small to form traditional charts.
Moving ranges are calculated by measuring the value-to-value differences.
Interpretation is the same - check trends, runs, patterns, limits
Control Charts

5. Moving-average and Moving-range
Plot moving-average
replace oldest value with newest value
sample size n = number of selected values
Moving-averages smooth out short-term variation
Lags occur, charts are less sensitive to change
Control Charts

6. All individual values Cluttered looking
Useful when examining individual variation
Control Charts

7. Median and Range charts
Median of the data is calculated and charted
Ease of calculation is a trade-off with some loss of sensitivity.
Constructed and interpreted like X-bar/R charts
Control Charts

8. Run charts
Used to monitor process changes associated with a particular characteristic over time.
Either variables or attribute data.
X-axis shows time.
Y-axis shows attribute/variable value.
Control Charts

9. Charts for variable sub-group size
Sub-group size coefficients must be recalculated
Each subgroup with a different sample size will have its own control limits plotted.
Con: lots of calculations!
Control Charts

10. Pre-control charts
Study and compare product produced with tolerance limits.
Control Charts