Applying Statistical Process Control to Clinical Data: An Illustration

Abstract

Preparation of this article was supported in part by funds from the New York State Office of Mental Retardation and Developmental Disabilities. We dedicate this artide to the memory of David Chambers, who was a teacher with profound insight into the principles of statistical process control. We are grateful to Scott Geller for editorial guidance and for comments from reviewers that helped shape our commentary so that it might address more dearly the needs of applied behavior analysts.Requests for reprints should be sent to

Effect of levetiracetam on human corticospinal excitability

“…21 To simplify the method, we modified it by using the statistical process control chart. 19,20 We calculated the means of rectified EMG amplitudes and consecutive difference of each point measurement during 100 milliseconds of the pretrigger period. From these values, the 95% limits of variability were derived from two sigma limits (1.77 ϫ mean consecutive deviation) below the mean value.…”

“…From these values, the 95% limits of variability were derived from two sigma limits (1.77 ϫ mean consecutive deviation) below the mean value. 19,20 These limits acted as a guide to determine objectively SP offset by observing how the poststimulus EMG, plotted on a simple graph, differs in variation from the prestimulus EMG (see figure 1).…”

“…18 SP duration was defined as the interval between the magnetic stimulus and the first reoccurrence of rectified voluntary EMG activity. Using the method of statistical process control chart, 19,20 the reoccurrence of voluntary EMG activity was defined as the returning of EMG amplitudes higher than the value of [mean Ϫ1.77 ϫ mean consecutive difference] in EMG data measured during 100 milliseconds before TMS in five or more of 10 consecutive measurements, which was calculated automatically by using a computerized program (figure 1). This value represents two sigma limits below the mean value, corresponding to the 95% limit of variability.…”

Consistent Visual Analyses of Intrasubject Data

“…This lack of a formal set of rules reportedly may lead to subjectivity and inconsistency (Kazdin, 1982). To address this criticism, researchers have proposed the use of structured criteria (e.g., Pfadt, Cohen, Sudhalter, Romanczyk, & Wheeler, 1992) or visual aids (e.g., Fisher, Kelley, & Lomas, 2003) to standardize analysis of single-case data. Despite these alternative methods of data analysis, visual inspection continues to be the predominant method of analysis for single-case data.…”

Control charts demonstrated limited utility for the monitoring of lung function in asthma

“…The use of SPC is well established in a broad range of contexts, for example, the American Thoracic Society laboratory procedures manual [3]; and monitoring of aviation components [4]. These charts have been suggested for use in monitoring of biological data [5,6] and in health care institutions [7], but most of the publications have been case reports [8,9]. Control charts have been successfully applied in some areas of monitoring of chronic disease, for example, for anticoagulation monitoring [10] for which commercial software is available.…”