Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You and Your Team.

Learn More →

A Counterargument to Encounter Frequency and Target Achievement: Measurement Variability

A Counterargument to Encounter Frequency and Target Achievement: Measurement Variability We offer an alternative explanation for the conclusion of the recent report by Morrison and colleagues1 that encounter frequency leads to apparent better control of glucose (hemoglobin A1c), blood pressure, and low-density lipoprotein cholesterol in patients with diabetes mellitus. While the authors have acknowledged that several forms of bias (including confounding) may affect their results, another important reason for the association between more frequent consultations and meeting targets is measurement variability. Each marker is subject to considerable random measurement variability.2-4 Because of random “highs,” those with more frequent measurements will more likely be mistakenly labeled as being uncontrolled. The exclusion of patients with “transient” highs partly mitigates this problem. Patients with borderline levels who have more frequent physician encounters are still more likely to be identified as uncontrolled compared with those with less frequent encounters. Even more problematic are the random “lows” for those who have been identified as being uncontrolled; again, the more measurements that are performed, the more likely that one of the measurements crosses under the target. The authors acknowledge the possibility of ascertainment bias and attempt to adjust for this by comparing the probability of target achievement at the end of 2 years for different encounter frequencies. This does not seem to address the problem fully: those with more measurements are still more likely to come under target within the 2-year period because of measurement variability. Furthermore, the definition of the outcome at 2 years is unclear and no quantitative results are presented. Interestingly, the strongest effect identified by Morrison and colleagues1 is for blood pressure control, which is the marker that has the most random measurement variability. We also note that adjustment for treatment intensification makes little difference in the association between encounter interval and target achievement: a surprising finding if more frequent encounters are truly having an effect on meeting the target. To assess the effect of the bias due to measurement variability, the authors could examine whether encounter interval is associated with patients going out of control: ie, for those with a low starting value in control, calculate the time until it goes above the treatment targets. If our hypothesis is correct, then more frequent visits would be associated with the patient going out of control—a finding that is best explained by random measurement variability. Back to top Article Information Correspondence: Dr Hayen, School of Public Health A27, The University of Sydney, NSW 2006, Australia (andrew.hayen@sydney.edu.au). Financial Disclosure: None reported. References 1. Morrison F, Shubina M, Turchin A. Encounter frequency and serum glucose level, blood pressure, and cholesterol level control in patients with diabetes mellitus. Arch Intern Med. 2011;171(17):1542-155021949161PubMedGoogle ScholarCrossref 2. Takahashi O, Farmer AJ, Shimbo T, Fukui T, Glasziou PP. A1C to detect diabetes in healthy adults: when should we recheck? Diabetes Care. 2010;33(9):2016-201720566678PubMedGoogle ScholarCrossref 3. Bell KJL, Hayen A, Macaskill P, et al. Monitoring initial response to angiotensin-converting enzyme inhibitor-based regimens: an individual patient data meta-analysis from randomized, placebo-controlled trials. Hypertension. 2010;56(3):533-53920625081PubMedGoogle ScholarCrossref 4. Glasziou PP, Irwig L, Heritier S, Simes RJ, Tonkin A.LIPID Study Investigators. Monitoring cholesterol levels: measurement error or true change? Ann Intern Med. 2008;148(9):656-66118458278PubMedGoogle Scholar http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

A Counterargument to Encounter Frequency and Target Achievement: Measurement Variability

Loading next page...
 
/lp/american-medical-association/a-counterargument-to-encounter-frequency-and-target-achievement-bwZN0t7F93
Publisher
American Medical Association
Copyright
Copyright © 2012 American Medical Association. All Rights Reserved.
ISSN
0003-9926
eISSN
1538-3679
DOI
10.1001/archinternmed.2011.807
Publisher site
See Article on Publisher Site

Abstract

We offer an alternative explanation for the conclusion of the recent report by Morrison and colleagues1 that encounter frequency leads to apparent better control of glucose (hemoglobin A1c), blood pressure, and low-density lipoprotein cholesterol in patients with diabetes mellitus. While the authors have acknowledged that several forms of bias (including confounding) may affect their results, another important reason for the association between more frequent consultations and meeting targets is measurement variability. Each marker is subject to considerable random measurement variability.2-4 Because of random “highs,” those with more frequent measurements will more likely be mistakenly labeled as being uncontrolled. The exclusion of patients with “transient” highs partly mitigates this problem. Patients with borderline levels who have more frequent physician encounters are still more likely to be identified as uncontrolled compared with those with less frequent encounters. Even more problematic are the random “lows” for those who have been identified as being uncontrolled; again, the more measurements that are performed, the more likely that one of the measurements crosses under the target. The authors acknowledge the possibility of ascertainment bias and attempt to adjust for this by comparing the probability of target achievement at the end of 2 years for different encounter frequencies. This does not seem to address the problem fully: those with more measurements are still more likely to come under target within the 2-year period because of measurement variability. Furthermore, the definition of the outcome at 2 years is unclear and no quantitative results are presented. Interestingly, the strongest effect identified by Morrison and colleagues1 is for blood pressure control, which is the marker that has the most random measurement variability. We also note that adjustment for treatment intensification makes little difference in the association between encounter interval and target achievement: a surprising finding if more frequent encounters are truly having an effect on meeting the target. To assess the effect of the bias due to measurement variability, the authors could examine whether encounter interval is associated with patients going out of control: ie, for those with a low starting value in control, calculate the time until it goes above the treatment targets. If our hypothesis is correct, then more frequent visits would be associated with the patient going out of control—a finding that is best explained by random measurement variability. Back to top Article Information Correspondence: Dr Hayen, School of Public Health A27, The University of Sydney, NSW 2006, Australia (andrew.hayen@sydney.edu.au). Financial Disclosure: None reported. References 1. Morrison F, Shubina M, Turchin A. Encounter frequency and serum glucose level, blood pressure, and cholesterol level control in patients with diabetes mellitus. Arch Intern Med. 2011;171(17):1542-155021949161PubMedGoogle ScholarCrossref 2. Takahashi O, Farmer AJ, Shimbo T, Fukui T, Glasziou PP. A1C to detect diabetes in healthy adults: when should we recheck? Diabetes Care. 2010;33(9):2016-201720566678PubMedGoogle ScholarCrossref 3. Bell KJL, Hayen A, Macaskill P, et al. Monitoring initial response to angiotensin-converting enzyme inhibitor-based regimens: an individual patient data meta-analysis from randomized, placebo-controlled trials. Hypertension. 2010;56(3):533-53920625081PubMedGoogle ScholarCrossref 4. Glasziou PP, Irwig L, Heritier S, Simes RJ, Tonkin A.LIPID Study Investigators. Monitoring cholesterol levels: measurement error or true change? Ann Intern Med. 2008;148(9):656-66118458278PubMedGoogle Scholar

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Feb 27, 2012

Keywords: ldl cholesterol lipoproteins,diabetes mellitus,consultation,blood pressure,glucose,hemoglobin a,blood pressure regulation

References