Quality Progress - August 2016 - (Page 52)

STATISTICS ROUNDTABLE BY JULIA E. SEAMAN AND I. ELAINE ALLEN Plotting for Quality Comparing devices using Bland-Altman, polar and 4-quadrant plots THERE ARE MANY ways to compare can reveal correlation and agreement, tinuous noninvasive blood pressure via new measurement devices to standards or as well as calculate the bias between the a pulse contour algorithm-called pulse other existing measurements. The most devices. decomposition analysis-compared to a basic way is to compare the raw values This column will describe how a new between the new device and standards, noninvasive device, the CareTaker (CT), or other devices measuring the same was tested and statistically proven using group-average accuracy and precision are outcomes. While easy, this approach has these plots to be within medical stan- defined as acceptable if bias is not greater many issues-from simply using differ- dards and equivalent to current invasive than 5 mmHg, and the standard deviation ent units or time scales to more complex measurements. is not greater than 8 mmHg. To validate radial arterial catheter. According to these standards, the problems when comparing the overall the new device, standard statistical meth- trend. A slightly more complex analysis Beginning the validation ods, including Bland-Altman plots,5 as To obtain U.S. Food and Drug Adminis- well as newer graphical techniques: four- includes correlation analysis between the tration approval for a new noninvasive quadrant and polar plots6, 7 were used. devices. Correlation shows the strength of monitor of arterial pressure, the device The results of the clinical study have been relation between the devices, but it does must satisfy the limits established for the published elsewhere.8 In this column, not reveal the strength of agreement and validation of automatic arterial-pressure however, the statistical method used for is prone to problems.1 Relatively simple monitoring by the Association for the approval of this device is examined. approaches to reveal agreement are con- Advancement of Medical Instrumentation structing a Bland-Alman plot (also known (AAMI).2 The ANSI/AAMI/ISO 81060- Methods of data collection as Tukey mean difference plot) or similar 2:2013 standards were used to evaluate Twenty-four patients scheduled for major four-quadrant and polar plots. These plots the CT device,4 which measures con- abdominal surgery consented to partici- 3 Correlation and Bland-Altman graphs Pearson's R Adj. R-square 120 0.87166 0.75975 20 10 MAP difference 100 A-line MAP Mean: -0.57 mmHg SD: 5.38 mmHg 15 110 90 80 70 60 50 / FIGURE 1 5 0 -5 -10 -15 -20 40 50 60 70 80 90 100 110 120 PDA MAP -25 50 60 70 Note: The correlation (top, linear fit with 95% confidence bounds) and (bottom) Bland Altman graphs are used for mean arterial pressure comparison of both blood pressure measurement systems. SD = standard deviation MAP = mean arterial pressure PDA = pulmonary diastolic arterial pressure 52 QP * www.qualityprogress.com 80 90 MAP average 100 110 http://www.qualityprogress.com

Table of Contents for the Digital Edition of Quality Progress - August 2016

Up Front
LogOn
Expert Answers
Keeping Current
Mr. Pareto Head
Chain Challenges
Sample Simplification
Recognize, Rate and Resolve
Exploiting Bottlenecks
Station to Station
Quality in the First Person
Career Corner
Statistics Roundtable
Standards Outlook
QP Toolbox
QP Reviews
One Good Idea
Back to Basics

Quality Progress - August 2016

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