Why These Disorders Are Not Diagnosed
As the authors point out, however, even the physicians in the highest quartile diagnose mental disorders in only 9% of their patients, which means that probably only one third of the patients meeting the criteria are identified by encounter diagnoses. Why are so many mental disorders not diagnosed? Is it just the particular diagnostic pattern we see here that is associated with low-cost behavior, or should we infer that diagnostic rates are generally associated with lower costs of care? There is no telling what would happen if a higher proportion of disorders were diagnosed or what would happen to expenditures in the low-diagnosis quartile if their diagnostic rate were somehow raised to 9%. We do not know if patients with those diagnoses are different from those who do not have such diagnosis, and if so, in what ways. I also question the physicians themselves. I am reminded of a practice that, compared with 2 similar practices, made fewer mental health diagnoses and scheduled far more diagnostic tests, medical consultations, and referrals. One observer said of this practice, “It’s easier to order tests than listen to the patient.” Thus, 2 threads of inquiry need to be followed up: (1) These patients may be unique in ways that affect the cost of their care—ways that may not apply to the larger pool of undiagnosed patients, and (2) the relationship between the diagnosis and expenditures may be confounded by a set of intervening physician-level behaviors that this study was not designed to capture. I agree with the authors’ conclusion that a fruitful next step would be to link diagnoses with expenditures at the patient level and to observe physician behavior for the presence of confounds.
We also do not know if the patients in the 4 groups are alike. The authors have undertaken a case-mix adjustment under the assumption that they are different. I accept their rationale for doing so, but this introduces a number of disturbing new factors into the interpretation of the results. The ambulatory diagnostic group methodology employed here contains mental health diagnoses, which means that the variable of interest is analyzed after its effects have been adjusted out. The logic for leaving the mental health diagnoses in the case-mix adjustment (apart from the reluctance to tamper with a validated instrument) are that the differences in mental health diagnoses are at least partly due to physician differences beyond any differences in actual rates of diagnosis, and adjusting will reveal, rather than obscure, those differences. This is a problem that should be pursued on the next iteration, with a design that does not require such an adjustment. Until our current ambulatory case-mix methodology has been sufficiently refined, such adjustments will introduce confusion into our research. It is critical that we clarify whether these physicians are practicing on panels of patients that are different or whether they are practicing differently on similar panels of patients.
The effect described in the study (lower expenditures with higher mental health diagnosis rates) would be most persuasive if it followed a linear pattern, but at least with respect to total costs, this effect is curvilinear: Expected costs fall from the lowest through the third quartile but then jump to a high in the fourth quartile. The actual costs were high in the first quartile, then fell and remained relatively flat through the other 3 quartiles. The difference after adjustment is significant. However, the pattern through the 4 quartiles does not describe a dose-response effect, and the pattern is not consistent across the outcomes examined in these analyses. The outcomes do not converge convincingly on a single pattern. This in no way invalidates the significance of the findings, but it does suggest that further refinements in design and analysis are desirable.
Thoughts for the Future
The study by Campbell and colleagues is extremely provocative and interesting and raises as many questions as it answers. It appears that physicians likely to place mental health diagnoses on an encounter form do so among patients who have lower health care costs. It is now up to us to learn whether this is actually true, and if so, why. Is it because these patients thereby become less expensive to care for? These patients are incidentally less expensive to care for? Physicians who record such diagnoses practice relatively less expensive medicine? These physicians attract and retain patients who are less expensive to care for? Or the case-mix adjustment has introduced an artifact? This is an interesting and important research agenda, and we are indebted to these researchers for putting it in such bold relief. If this finding is replicated, we will need to discover ways to magnify the result by supporting the particular behavior responsible for it, and to test whether it has the same effects in those patients who are affected but have not been given a mental diagnosis. Then we will be closer to our goal of practicing coherent integrated primary care in which mental and medical health are approached as 2 facets of the same stone.