Motion sickness incidence: distribution of time to first emesis and comparison of some complex motion conditions.

A statistical mixture model is used to fit time-to-emesis data. The Weibull probability distribution is shown to provide a good fit for those subjects who either become sick or withdraw from the experiment within 2 h. The second part of the mixture accounts for those subjects who neither quit nor vomit within 2 h. The log-normal probability model is shown to give a poorer fit to the data and figures showing the relative fits of the estimated Weibull and log-normal distributions are provided. A nonparametric test is used to compare the five motion conditions of the Correlation Study. That test shows that there are significant differences in severity among the conditions.