Globus pallidus interna versus subthalamic nuclues Deep Brain Stimulaiton
Erwin B.Montgomery Jr. MD, Professor, University of Alabama at Birminghamemontgom@uab.edu
Submitted July 13, 2012
Weaver et al. [1] and Tagliati [2] mistakenly infer clinical equivalence between globus pallidus interna versus subthalamic nucleus deep brain stimulation based on failure to demonstrate statistically significant differences. [3] A clinically meaningful—not statistically significant— difference in outcome should be decided a priori, after which the sample size necessary to have a reasonable probability of detecting the difference could be determined. [4] Fortunately, the study by Weaver et al. had sufficient sample size to demonstrate a 1-point difference in motor outcomes. However, such comparisons presume optimal management so as not to produce a "ceiling effect" that would obscure differences.
While probably unintended, Tagliati may be undervaluing personal preference [5] which ideally reflects the necessary reasoned judgment experts use toward the diverse factors that influence potential outcomes for their individual patients. This includes factors beyond those mentioned in the study by Weaver et al., such as the relative ease and safety of surgical approaches when microelectrode recordings are used for target localization. There is no simple calculus to address all these factors, and even if there were, application to an individual patient would be problematic. [5] In the end, personal preference--if it is reasoned expert judgment--will always trump statistical inference.
1. Weaver FM, Follett KA, Stern M, et al. Randomized trial of deep brain stimulation for Parkinson disease: Thirty-six-month outcomes. Neurology 2012;79:55-65.
2. Tagliati M. Turning tables: Should GPi become the preferred DBS target for Parkinson disease? Neurology 2012;79:19-20.
3. Altman DG, Bland JM. Absence of evidence is not evidence of absence. BMJ 1995;311:485.
4. Wellek S. Testing Statistical Hypotheses of Equivalence and Noninferiority, Second ed. Boca Raton: CRC Press, 2010.
5. Montgomery EB Jr, Turkstra LS. Evidenced Based Medicine: Let's be reasonable. Journal of Medical Speech Language Pathology 2003;11:ix-xii.
Weaver et al. [1] and Tagliati [2] mistakenly infer clinical equivalence between globus pallidus interna versus subthalamic nucleus deep brain stimulation based on failure to demonstrate statistically significant differences. [3] A clinically meaningful—not statistically significant— difference in outcome should be decided a priori, after which the sample size necessary to have a reasonable probability of detecting the difference could be determined. [4] Fortunately, the study by Weaver et al. had sufficient sample size to demonstrate a 1-point difference in motor outcomes. However, such comparisons presume optimal management so as not to produce a "ceiling effect" that would obscure differences.
While probably unintended, Tagliati may be undervaluing personal preference [5] which ideally reflects the necessary reasoned judgment experts use toward the diverse factors that influence potential outcomes for their individual patients. This includes factors beyond those mentioned in the study by Weaver et al., such as the relative ease and safety of surgical approaches when microelectrode recordings are used for target localization. There is no simple calculus to address all these factors, and even if there were, application to an individual patient would be problematic. [5] In the end, personal preference--if it is reasoned expert judgment--will always trump statistical inference.
1. Weaver FM, Follett KA, Stern M, et al. Randomized trial of deep brain stimulation for Parkinson disease: Thirty-six-month outcomes. Neurology 2012;79:55-65.
2. Tagliati M. Turning tables: Should GPi become the preferred DBS target for Parkinson disease? Neurology 2012;79:19-20.
3. Altman DG, Bland JM. Absence of evidence is not evidence of absence. BMJ 1995;311:485.
4. Wellek S. Testing Statistical Hypotheses of Equivalence and Noninferiority, Second ed. Boca Raton: CRC Press, 2010.
5. Montgomery EB Jr, Turkstra LS. Evidenced Based Medicine: Let's be reasonable. Journal of Medical Speech Language Pathology 2003;11:ix-xii.
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