The validation of biodynamic models

Biodynamic models may: (i) represent understanding of how the body moves (i .e., 'mechanistic models'), (ii) summarise biodynamic measurements (i.e., ' quantitative models'), and (iii) provide predictions of the effects of moti on on human health, comfort or performance (i.e.,'effects models'). Model validation may involve consideration of evidence used to derive a mod el, comparison of the model with alternatives, and a comparison between mod el predictions and independent observations of the predicted qualities or q uantities. Models should be associated with a specified range of independen t and dependent variables and indicate how intra-subject variability and in ter-subject variability are accommodated. Models of the mechanisms of body movement may be validated by demonstrations that the mechanisms are well re presented. Models giving numerical predictions ('quantitative models' and ' effects models') should specify the expected accuracy of predictions. 'Effe cts models' advocated for predicting health, comfort or performance require that: (i) vibration or shock is a proven cause of the specified effect, (i i) within all reasonable ranges of model inputs, there must be reason to ex pect a positive correlation and acceptable error between the model predicti ons and the effect, (iii) other variables having a large influence on the e ffect must be taken into consideration. It is more useful to report the acc uracy of 'quantitative models' and 'effects models' models than to state th at they are 'validated' or 'un-validated'. Checklists for assessing the quality of a biodynamic model are proposed, ta king into account the type of model and the model assertions, the evidence, the assumptions, the accuracy, and the appropriateness of the model.