This information is valuable in seeking to explain earnings mobility. Particular interest attaches to material on the person’s work career: profession, employer, experience, changes of job. Job information is however difficult to handle: a person could have changed job ten times in a year, and have had periods of unemployment in between. Studies which have contained this kind of information include the NSF data on scientists in the US, the study of chemists in Britain by Creedy, and the NLS panels in the US, where labour market activity was a particular focus.