Letters to the Editor
Response to a Letter From Dr. Timothy A. DeRouen We are pleased to clarify the points raised in Dr. DeRouen’s letter, which serves to remind us that patient-centered biomedical research always proceeds without perfect knowledge and control. Although the definition of “treated” in our study was indeed stringent, it was derived from analysis, not set arbitrarily. The observation that fewer than four visits did not yield as strong an effect may help explain why some other studies have found that the mere fact of periodontal treatment, irrespective of its effectiveness, may offer few systemic health benefits. We, too, are concerned by the surprisingly low fraction of patients receiving treatment at what seems to be the “minimal effective dose.” It is reasonable to speculate that differences in health outcomes might be due in part to different propensities to seek or comply with medical advice. Although individual behavior clearly does vary in this respect, it cannot explain all the observed outcomes in this study. The fact that the medical costs for the two treatment groups were statistically indistinguishable prior to the intervention (Figure 2) is sufficient evidence that preexisting group characteristics, including but not limited to behavioral propensities, cannot account for differences in this primary outcome. Such striking de facto similarity between the two groups in our study was unexpected but real, and in no way diminishes the validity of the comparisons; obviously, other populations may not exhibit this feature. More generally, no study—even the best-designed RCT—can hope to capture, let alone control for, all the parameters that have the potential to influence the chosen outcomes. Some go unrecorded, some are unrecognized, and some are dismissed by the researcher as unimportant. The problem is especially severe in studies
& 2015 American Journal of Preventive Medicine
of historic databases, where many possibly important variables simply do not make it into the record. These limitations do not invalidate such methods, properly executed, but they do place a premium on cautious and insightful interpretation of the results. Our paper reported the factual results of a retrospective study of data recorded for other purposes, and did not propose causative mechanisms. We did not suggest, nor do we believe, that explanations should be sought exclusively among organic mechanisms: it is entirely plausible (and consistent with the multi-year response we observed) that the very experience of completing a lengthy course of periodontal therapy might have a lasting impact on an individual’s approach to health care in general. Judicious clinical decision making must take account of well-documented “input– output” relationships, whether or not a mechanism is clear. We wholeheartedly agree with Dr. DeRouen that the effectiveness of any therapy is influenced by a host of causes, whose characterization and manipulation are prime research goals. But absent a perfect data set— where all possible clinical and economic outcomes are measured uniformly over many years, in large, diverse, and exhaustively characterized populations—the public’s health can perhaps be better served by exploiting available data, warts and all, than by waiting indefinitely for the “definitive” answer. Marjorie Jeffcoat, DMD School of Dental Medicine, University of Pennsylvania Philadelphia, Pennsylvania http://dx.doi.org/10.1016/j.amepre.2014.11.011
No financial disclosures were reported by the authors of this paper.
Published by Elsevier Inc.
Am J Prev Med 2015;48(3):e5 e5
Response to a Letter From Dr. Timothy A. DeRouen We are pleased to clarify the points raised in Dr. DeRouen’s letter, which serves to remind us that patient-centered biomedical research always proceeds without perfect knowledge and control. Although the definition of “treated” in our study was indeed stringent, it was derived from analysis, not set arbitrarily. The observation that fewer than four visits did not yield as strong an effect may help explain why some other studies have found that the mere fact of periodontal treatment, irrespective of its effectiveness, may offer few systemic health benefits. We, too, are concerned by the surprisingly low fraction of patients receiving treatment at what seems to be the “minimal effective dose.” It is reasonable to speculate that differences in health outcomes might be due in part to different propensities to seek or comply with medical advice. Although individual behavior clearly does vary in this respect, it cannot explain all the observed outcomes in this study. The fact that the medical costs for the two treatment groups were statistically indistinguishable prior to the intervention (Figure 2) is sufficient evidence that preexisting group characteristics, including but not limited to behavioral propensities, cannot account for differences in this primary outcome. Such striking de facto similarity between the two groups in our study was unexpected but real, and in no way diminishes the validity of the comparisons; obviously, other populations may not exhibit this feature. More generally, no study—even the best-designed RCT—can hope to capture, let alone control for, all the parameters that have the potential to influence the chosen outcomes. Some go unrecorded, some are unrecognized, and some are dismissed by the researcher as unimportant. The problem is especially severe in studies
& 2015 American Journal of Preventive Medicine
of historic databases, where many possibly important variables simply do not make it into the record. These limitations do not invalidate such methods, properly executed, but they do place a premium on cautious and insightful interpretation of the results. Our paper reported the factual results of a retrospective study of data recorded for other purposes, and did not propose causative mechanisms. We did not suggest, nor do we believe, that explanations should be sought exclusively among organic mechanisms: it is entirely plausible (and consistent with the multi-year response we observed) that the very experience of completing a lengthy course of periodontal therapy might have a lasting impact on an individual’s approach to health care in general. Judicious clinical decision making must take account of well-documented “input– output” relationships, whether or not a mechanism is clear. We wholeheartedly agree with Dr. DeRouen that the effectiveness of any therapy is influenced by a host of causes, whose characterization and manipulation are prime research goals. But absent a perfect data set— where all possible clinical and economic outcomes are measured uniformly over many years, in large, diverse, and exhaustively characterized populations—the public’s health can perhaps be better served by exploiting available data, warts and all, than by waiting indefinitely for the “definitive” answer. Marjorie Jeffcoat, DMD School of Dental Medicine, University of Pennsylvania Philadelphia, Pennsylvania http://dx.doi.org/10.1016/j.amepre.2014.11.011
No financial disclosures were reported by the authors of this paper.
Published by Elsevier Inc.
Am J Prev Med 2015;48(3):e5 e5
