The Implications of Measuring Complexity

Lee A. Green

doi:10.1370/afm.1147

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Complexity, whether patient or visit
Lee A Green

Published on: 03 August 2010
Complexity of patient illness versus complexity of patient visits
Barbara Starfield

Published on: 02 August 2010

Published on: (3 August 2010)
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Complexity, whether patient or visit
Lee A Green, Ann Arbor, MI, USA
Starfield and Lemke point out distinctions between their intended uses of the ADG/ACG system and Katerndahl, Wood, & Jaen's examination of within-visit complexity. However, my accompanying editorial was not limited to issues of within-visit complexity. Rather, my concern is the impact of how the work of primary care is measured upon the management and policy decisions that are driven by those measures. The ADG/ACG we...
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Starfield and Lemke point out distinctions between their intended uses of the ADG/ACG system and Katerndahl, Wood, & Jaen's examination of within-visit complexity. However, my accompanying editorial was not limited to issues of within-visit complexity. Rather, my concern is the impact of how the work of primary care is measured upon the management and policy decisions that are driven by those measures. The ADG/ACG website itself promotes the ACG system for uses including "evaluating provider performance and setting equitable payment rates", and hence its application does directly impact the measurement and valuation of primary care work.
As Starfield and Lemke point out, the ADGs themselves are categorical. However, in concluding that that means ADGs are "not linear", they appear to confound linear systems with simple continuous linear equations. ADGs are described in the relevant publications as having been derived from multivariate modeling techniques, and when applied for their expressly intended quantitative purposes such as performance evaluation they are being used as categorical variables in multivariate statistical models. Hence both in derivation and application, the ADG/ACG system is grounded in linear stochastic mathematics, dependent upon assumptions such as the Central Limit Theorem that do not hold in complex nonlinear systems. That does not in any way detract from the ADG/ACG system's sophistication nor the value of its patient-centered method, it merely describes the fundamental mathematics upon which the system is based and contrasts them to complex nonlinear dynamics.
There are two important implications that matter greatly in the management of health care and in the formulation of health policy as we make major changes to the system. First, previously accurate statistical models may suddenly deliver misleading results. Second, even when they accurately represent the behavior of the system, statistical models' equations may not be at all representing how the system produces that behavior, and hence may mislead us as to how to change it. Both of these concerns are of course dependent upon the "if" in the editorial: if primary care is a complex nonlinear system. Hence the importance of work such as Katerndahl, Wood, & Jaen's, exploring alternatives to linear stochastic models.
Competing interests: None declared
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Competing Interests: None declared.
Published on: (2 August 2010)
Page navigation anchor for Complexity of patient illness versus complexity of patient visits
Complexity of patient illness versus complexity of patient visits
Barbara Starfield, Baltmore, MD, USA
Other Contributors:
In his editorial concerning the article by Dr. Katerndahl et al, Dr, Green asserts that the Ambulatory Diagnostic Groups are based on a ‘linear model and (is) not only inaccurate..fundamentally wrong as a measure of primary care.’ His comment reflects a lack of understanding of the Ambulatory Diagnostic Groups and the larger system of which it is a part. (For information about the system, see www.acg.jhsph.edu). The ADG...
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In his editorial concerning the article by Dr. Katerndahl et al, Dr, Green asserts that the Ambulatory Diagnostic Groups are based on a ‘linear model and (is) not only inaccurate..fundamentally wrong as a measure of primary care.’ His comment reflects a lack of understanding of the Ambulatory Diagnostic Groups and the larger system of which it is a part. (For information about the system, see www.acg.jhsph.edu). The ADG approach groups diagnoses by their clinical type, primarily (but not only) on the basis of their likelihood of persistence. There is nothing quantitative about this and ADGs cannot be ‘linear’ in the statistical meaning of the term. The Adjusted Clinical Groups (ACGs) carry this categorization one step further by deriving about 100 different combinations of the 32 ADGs to provide an estimate of morbidity in individuals and populations over time. ACGs are not ‘linear’, and their purpose is to describe patient complexity of illness based on the pattern of different types of morbidity over a period of time. Dr. Green uses the terminology ‘complex’, ‘linear’, and ‘non-linear’ differently than most statisticians would. The implication that a linear model is any model that isn’t generated by complexity science would be a distortion.
Dr. Katerndahl’s intriguing measure of complexity is a measure of VISIT complexity whereas the ACG system (of which ADGs are one part) is a measure of the complexity of patient’s (and, by aggregation population) diagnostic complexity over a period of time. Whereas the Katerndahl et al measure of complexity of visits seems to be an innovative approach to provider reimbursement, it is not intended to and does not describe the burden of morbidity experienced by patients and populations. Whereas the Katerndahl et al measure could be used as a basis for developing a reimbursement strategy for VISITS to different types of specialists, the ADGs (and ACGs) would not be used that way, since they are PERSON-FOCUSED over time; they might be used to in a time-based reimbursement system dependent on patient and population morbidity burden. Contrary to the assumption made by Dr. Green, we are not aware of any attempt to use ADGs to pay for visits. We believe that the ACG system has much potential for documenting the increased challenges of primary care (as distinguished from other specialty care) but in a different and complementary way than that developed by Katerndahl and colleagues. Indeed, we hope that family physicians and other primary care practitioners come to appreciate how the ACG system can further buttress arguments for the increased importance of primary care.
Barbara Starfield
Klaus Lemke
References: Green L. The implications of measuring complexity. Ann Fam Med 2010; 8:291-2
Katerndahl D, Wood R, Jaen C. A method for estimating relative complexity of ambulatory care. Ann Fam Med 2010; 8: 341-47
Competing interests: Both Starfield and Lemke have and continue to be involved in deveoping the Johns Hopkins Adjusted Clinical Groups (ACGs). Neither have equity in the entities licensing or selling the software.
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Competing Interests: None declared.