Evaluation of Internet-delivered continuing education for health care providers requires appropriate consideration of their level of participation. To fully assess participation requires multidimensional measures, including factors such as the volume of participation (page views), frequency (visits), variety (components accessed by each provider), and duration (months of activity). We calculated crude and refined (adjusted for study design) measures and then compared these measures across three longitudinal Internet-delivered continuing education to health care providers (N = 429). We found that participation varied across study, varied by factor and varied by specific measure. Correlation between crude and refined measures within a factor and across factors differed significantly. Participation assessment of internet-delivered interventions varies by the selection of measure and factor. Further research assessing the potential for these measures to predict intervention effectiveness is needed. © 2007 The authors. All rights reserved.