Mark van de Ruit1, Michael J Grey2. 1. Department of Biomechanical Engineering, Delft University of Technology, Delft, the Netherlands. 2. Acquired Brain Injury Rehabilitation Alliance, School of Health Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK. Electronic address: m.grey@uea.ac.uk.
Abstract
BACKGROUND: A trend in the non-invasive brain stimulation literature is to assess the outcome of an intervention using a responder analysis whereby participants are di- or trichotomised in order that they may be classified as either responders or non-responders. OBJECTIVE: Examine the extent of the Type I error in motor evoked potential (MEP) data subjected to responder analyses. METHODS: Seven sets of 30 MEPs were recorded from the first dorsal interosseous muscle in 52 healthy volunteers. Four classification techniques were used to classify the participants as responders or non-responders: (1) the two-step cluster analysis, (2) dichotomised thresholding, (3) relative method and (4) baseline variance method. RESULTS: Despite the lack of any intervention, a significant number of participants were classified as responders (21-71%). CONCLUSION: This study highlights the very large Type I error associated with dichotomising continuous variables such as the TMS MEP.
BACKGROUND: A trend in the non-invasive brain stimulation literature is to assess the outcome of an intervention using a responder analysis whereby participants are di- or trichotomised in order that they may be classified as either responders or non-responders. OBJECTIVE: Examine the extent of the Type I error in motor evoked potential (MEP) data subjected to responder analyses. METHODS: Seven sets of 30 MEPs were recorded from the first dorsal interosseous muscle in 52 healthy volunteers. Four classification techniques were used to classify the participants as responders or non-responders: (1) the two-step cluster analysis, (2) dichotomised thresholding, (3) relative method and (4) baseline variance method. RESULTS: Despite the lack of any intervention, a significant number of participants were classified as responders (21-71%). CONCLUSION: This study highlights the very large Type I error associated with dichotomising continuous variables such as the TMS MEP.