Convert these numbers into the average moving ranges
and voil? , you can build an XmR chart.
u-Charts
The u-chart is based on the assumption that your data are based on a count of
discrete events occurring within well-defined, finite regions/areas, and that these
events are independent. The u-chart assumes a Poisson process. You may want
to consider a u-chart when dealing with defects (counts) within a group of pages
(region/area), for example, number of errors per page or the number of defects per
1,000 lines of code.
The u-chart differs from the XmR in that the upper and lower control limits of
the u-chart change over time. The ?« in u-chart is the weighted average of the count
(?« = ??countj / ??sizej). The upper control limit is calculated by adding ?« to three
times the square root of the ?« divided by the last size (sizej). The lower control limit
is calculated by subtracting ?« from three times the square root of the ?« divided by
the last size (sizej).
Now then, let??™s go back and look at our example of inconsistent data gathered
from peer reviews.
Pages:
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543