An article in Quality & Safety in Health Care [Statistical Process Control as a Tool for Research

An article in Quality & Safety in Health Care [€œStatistical Process Control as a Tool for Research and Healthcare Improvement,€ (2003 Vol. 12, pp. 458€“464)] considered a number of control charts in healthcare. An X chart was constructed for the amount of infectious waste discarded each day (in pounds). The article mentions that improperly classified infectious waste (actually not hazardous) adds substantial costs to hospitals each year.

The following tables show approximate data for the average daily waste per month before and after process changes, respectively. The process change included an education campaign to provide an operational definition for infectious waste.

(a) Handle the data before and after the process change separately and construct individuals and moving-range charts for each set of data. Assume that assignable causes can be found and eliminate suspect observations. If necessary, revise the control limits.

(b) Comment on the control of each chart and differences between the charts. Was the process change effective?

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Before Process Change 2 3 Month 1 4 5 9. Waste 6.9 6.8 6.9 6.7 6.9 7.5 7.4 7 Month 13 14 15 16 17 18 19 20 21 Waste 7.5 7.4 6.5 6.9 7.0 7.2 7.8 6.3 6.7 After Process Change Month 1 2 3 4 5 6 7 8 9 10 11 12 Waste 5.0 4.8 4.4 4.3 4.6 4.3 4.5 3.5 4.0 4.1 3.8 5.0 Month 13 14 15 16 17 18 19 20 21 22 23 24 Waste 4.6 4.0 5.0 4.9 4.9 5.0 6.0 4.5 4.0 5.0 4.5 4.6 Month 25 26 27 28 29 30 Waste 4.6 3.8 5.3 4.5 4.4 3.8