There are hundreds of assessment tools available now to individuals, recruiters and human resources personnel, thanks to some early work that started in 444 BC. At this time, Empodocles, the founder of the school of medicine in Sicily, categorised behavioural elements in terms of earth, air, fire and water. About 100 years later, Hippocrates determined that four ‘humours' of blood, yellow bile, phlegm and black bile were each thought to be responsible for a different type of personality. Over the centuries some of these descriptors have changed, however the work to understand people and how they tick, continues. Carl Jung, in 1923, described people's ‘types' in terms of Feeler, Intuitor, Thinker and Sensor – the foundation for the Myer's Briggs Type Indicator (MBTI). The basis for the DiSC assessment emerged from William Marston and his research on the emotions of people, in 1928.