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Fig. 3 | BMC Family Practice

Fig. 3

From: The impact of a prescription review and prescriber feedback system on prescribing practices in primary care clinics: a cluster randomised trial

Fig. 3

p-charts illustrating the percentage of prescriptions with error over the 8-month study period. The line with data markers represents the percentage of prescriptions with error at each time point. The central line corresponds to the process mean (average percentage of prescriptions with errors). The control limits (dotted lines) were calculated based on a normal approximation of the binomial distribution, and positioned at a distance of three standard deviations (SD) around the central line. The upper control limit was calculated by adding three times the SD to the process mean. The lower control limit was calculated by subtracting three times the SD from the process mean. The control limits for each time point was calculated based on its specific sample size (number of prescriptions), and drawn in stair-steps to reflect the changes in sample size over time. Data points within the control limits suggest common-cause variation, and data points outside the control limits suggest special-cause variation. There was a delay in the delivery of prescribing performance feedback in September and November 2012. Prescribing performance feedback reports for September 2012 and November 2012 were delivered together with the reports for October 2012 and December 2012, respectively

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