SU MMARYAs with any measurement procedure, the performance of a subjective classification procedure must be evaluated. Observers have to be trained and their performance has to be assessed, preferably on a regular basis, to guarantee sufficient consistency and accuracy of classification results. The current paper is a study of observer performance where observers were asked to classify the gait of cows from video recordings. Gait was classified in nine ordered categories (ranging from 1=normal gait to 9=severely abnormal gait) and also as a continuous fraction by putting a mark on a paper strip (the left end corresponding to 0=normal gait and the right end to 1=severely abnormal gait). The use of statistical models and methodology for analysis of these visual scores is demonstrated and discussed. Observers were assessed by comparing their classification results with the results of an expert. Models and methodology take proper account of typical features of the data, i.e. the fact that data are discrete scores or continuous scores with an upper and lower bound, the variance heterogeneity and non-linearity of model terms that arises from this, and the dependence between repeated classifications of videos of the same cow. Results of the analyses are summarized in simple tables and plots. These are useful tools to indicate possible flaws in judgement of an observer, that may be corrected by further training. When a high standard is developed, which usually takes the form of the opinion of one or more experts, this methodology can be applied prior to any experiment where responses are ordered subjective scores.

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BACKGROUND:Medical educational research highlights the need for high-fidelity, multidisciplinary simulation training to teach complex decisionmaking skills, such as those taught in Advanced Trauma Life Support (ATLS). This approach is, however, expensive and timeintensive. Virtual reality (VR) education simulation may improve skill acquisition in a cost-effective and time-sensitive manner.We developed a novel trauma VR simulator (TVRSim) for providers to apply ATLS principles. We hypothesized in this pilot study that TVRSim could differentiate practitioner competency with increasing experience and would be well accepted. METHODS:Providers at a Level I trauma center (acute care surgeons, novice (MS4 & PGY1), junior (PGY2 & 3), senior (PGY4-6) residents) ran a blunt, polytrauma VR code. Ten critical decision points were assessed: intubation, cricothyroidotomy, chest tube, intravenous access, focused abdominal sonography for trauma examination, pelvic binder, activation of massive transfusion protocol, administration of hypertonic saline, hyperventilation and decision to go to the operating room (OR). Learner assessment was based on frequency and time to correct decisions. Participant satisfaction was measured using validated surveys. RESULTS:All 31 providers intubated and obtained intravenous access. Novices and juniors frequently failed at hypertonic saline and hyperventilation decisions. Juniors often failed at cricothyroidotomy (60%) and OR (100%) decisions. Mean time to all decisions except going to the OR was longer for all groups compared to acute care surgeons. Mean number of decisions/min was significantly higher for surgeons and seniors compared to juniors and novices. Mortality was 92.3% for novices, 80% for juniors, 25% for seniors and 0% for the attendings. Participants found TVRSim comfortable, easy to use/interact with/performance enhancing, and helped develop skills and learning. CONCLUSIONS:In this pilot study using a sample of convenience, TVRSim was able to discern decision-making abilities among trainees with increasing experience. All trainees felt that the platform enhanced their performance and facilitated skill acquisition and learning.TVRSim could be a useful adjunct to teach and assess ATLS skills.