Increasing the Validity and Efficiency of Blood Pressure Estimates Using Ambulatory and Clinic Measurements and Modern Missing Data Methods

original contributions nature publishing group Increasing the Validity and Efficiency of Blood Pressure Estimates Using Ambulatory and Clinic Measurements and Modern Missing Data Methods Matthew J. Zawadzki 1 , John W. Graham 2 and William Gerin 2 were available for ABPM and CBP, as well as an echocardiographic measure of left ventricular mass (LVM). Results Based on an estimated fivefold difference in cost for using ABPM compared to CBP, we found that statistical power can be considerably increased, or that BP measurement costs can be considerably reduced, when using this planned missing data design. Conclusions These benefits were observed with no loss of predictive validity (i.e., the observed association between BP and LVM). This suggests that the TMM design is a promising technique that in some studies may be able to decrease costs and/or increase one’s power to detect effects. Methods We applied the TMM approach, which makes use of a “bias correction” structural equation model, to an empirical data set in which data The problem of blood pressure measurement Two or more approaches are often taken to measure blood pres- sure (BP) as an outcome in empirical research. Measurements taken by the physician, nurse, or technician (clinic BP (CBP)), or taken using ambulatory BP monitoring (ABPM). Although the measures ostensibly tap the same construct (BP), ABPM is con- sidered the “gold standard” for BP measurement, as it is superior to CBP in terms of reliability and construct validity (i.e., ability to predict outcomes). This situation applies not only to BP, but to any construct that is assessed using more than one measure. CBP measurements. A strength of CBP is that it can be done quickly and inexpensively. Based on clinic readings, c ­ linicians make imme- diate decisions about a treatment plan, or the need for additional testing. However, these measurements provide only a “snapshot” 1 Department of Psychology, The Pennsylvania State University, University Park, Pennsylvania, USA; 2 Department of Biobehavioral Health, The Pennsylvania State University, University Park, Pennsylvania, USA. Correspondence: William Gerin (wxg17@psu.edu) Received 9 September 2011; first decision 11 October 2011; accepted 29 February 2012. © 2012 American Journal of Hypertension, Ltd. Keywords: ambulatory blood pressure; blood pressure; clinic blood pressure ; hypertension; missing data; two-method measurement design American Journal of Hypertension, advance online publication 19 April 2012; doi:10.1038/ajh.2012.40 of the BP when measured in the physician’s office or the clinic, circumstances that are atypical of the patient’s normal environ- ment. As a result, these measures are subject to biases, notably white coat hypertension, which requires ABPM to detect. ABPM strengths. ABPM involves the use of a portable device (typically worn for 24 h). Multiple measurements are taken throughout the day and often throughout the night. ABPM has been shown to be a better predictor of target organ dam- age and cardiovascular events than CBP. 1 In addition, ABPM is the most reliable way to detect masked hypertension, a condition in which patients’ BPs are normal in the physician’s office, but in the hypertensive range in their normal lives; as a result, they are undiagnosed and untreated. 2 The superior pre- dictive power of ABPM is likely due not only to the increased number of readings it provides, which increases reliability of the measure, but also to its ability to capture the impact of stressors and other environmental factors that occur in daily life and which are likely to affect the BP. 3,4 ABPM weaknesses. All things being equal, one would use ABPM in preference to CBP. However, although clearly a useful july 2012 | VOLUME 25 NUMBER 7 | 764-769 | AMERICAN JOURNAL OF HYPERTENSION Downloaded from http://ajh.oxfordjournals.org/ at University of California, Merced on November 24, 2014 Background Ambulatory blood pressure monitoring (ABPM) is considered the gold standard for BP measurement, compared to clinic BP measurements (CBP), which are a less valid predictor of target organ damage and cardiovascular events. However, ABPM is considerably more expensive than CBP, leaving BP researchers with a difficult dilemma: Use the less efficient CBP measure, or bear the cost of the more expensive ABPM. Recent developments in missing data methods, notably the two-method measurement (TMM) design, address this problem. With the TMM design, all research participants receive the less expensive CBP measure, but only a random subset receives the more expensive ABPM. The total number of participants must be increased, with additional participants receiving only CBP measurements. Even so, the TMM still reduces costs.