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ABSTRACT
It has been argued that neuropsychological studies generally possess adequate statistical power to detect large effect sizes. However, low statistical power is problematic in neuropsychological research involving clinical populations and novel interventions for which available sample sizes are often limited. One notable example of this problem is evident in the literature regarding the cognitive sequelae of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in persons with Parkinson's disease (PD). In the current review, a post hoc estimate of the statistical power of 30 studies examining cognitive effects of STN DBS in PD revealed adequate power to detect substantial cognitive declines (i.e., very large effect sizes), but surprisingly low estimated power to detect cognitive changes associated with conventionally small, medium, and large effect sizes. Such wide spread Type II error risk in the STN DBS cognitive outcomes literature may affect the clinical decision-making process as concerns the possible risk of postsurgical cognitive morbidity, as well as conceptual inferences to be drawn regarding the role of the STN in higher-level cognitive functions. Statistical and methodological recommendations (e.g., meta-analysis) are offered to enhance the power of current and future studies examining the neuropsychological sequelae of STN DBS in PD.
Notes
Note. These data reflect post hoc statistical power estimates generated using standard effect size conventions (cf. observed effect sizes), which were adapted from Cohen (Citation1988) and Zakzanis (Citation2001). Cohen's f values [f = (σm)/σ] reflect the SD of the standardized means in a population (Cohen, Citation1988). DBS = deepbrain stimulation; IQR = interquartile range; PD = Parkinson's disease; STN = subthalamic nucleus.
Note. N = 14; DBS = deep brain stimulation; IQR = interquartile range; PD = Parkinson's disease; STN = subthalamic nucleus. Cohen's f values [f = (σm)/σ] reflect the SD of the standardized means in a population (Cohen, Citation1988).