External body characteristics can very fairly systematically across population. For example, men tend to be, on average, taller and heavier than women. Similarly, certain ethnic groups may differ anthropometrically from others. This sort of information is often essential when designing products for sale to different population. It seems to be an accepted norm within human factors that products should be designed so that they fit - in terms of, foe example, strength and anthropometrics 95 per cent of the people for whom they are designed.