Methodology:

Data for the time series on median pay of major occupation groups was taken from the ONS website and can be found here. It is important to note that in this timeseries the data for 2017 is provisional. Data on the median pay of specific occupations was taken from the ONS website here and uses the revised 2017 data published in 2018. Both data sets only sampled people working fulltime on adult rates for a single company who had been there for at least a year. Full time is clasified as 30 hours per week (or 25 hours for teaching proffessions).

The median is the value at which 50% of the population lies on either side. The median has been used rather than the mean as it is a better representation of the incomes of most people in that occupation or group. This is due to the presence of a relatively small number of much higher incomes that skew the mean to a higher value that is not necessarily representative of typical incomes. Some occupations were omitted as either the median statistic was not applicable or the median itself was considered unreliable. These omissions were done by the ONS as their coefficient of variation (CV) was above 20% and thus were not judged as reliable estimates of the typical income in the respective category. The coefficient of variation, also knows as the relative standard deviation, is the ratio of the standard error of an estimate to the estimate itself.

The occupations omitted because the median income statistic was not applicable are: Coal mine operatives, Dancers and choreographers, Market and street traders and assistants, NCOs and other ranks, Officers in armed forces, and Smiths and forge workers.

The occupations omitted because their median income estimates were unreliable (CV > 20%) are: 'Actors, entertainers and presenters', 'Authors, writers and translators', 'Barristers and judges', 'Boat and ship builders and repairers', 'Brokers', 'Chartered architectural technologists', Collector salespersons and credit agents', 'Dental practitioners', 'Dispensing opticians', 'Driving instructors', 'Elected officers and representatives', 'Industrial cleaning process occupations', 'Leisure and theme park attendants', 'Managers and proprietors in forestry, fishing and related services', 'Market research interviewers', 'Moulders, core makers and die casters', 'Other drivers and transport operatives','Other elementary services occupations', 'Plastics process operatives', 'Podiatrists', 'Publicans and managers of licensed premises', 'Quarry workers and related operatives', 'Senior officers in fire, ambulance, prison and related services', 'Ship and hovercraft officers', 'Shopkeepers and proprietors' – 'wholesale and retail', 'Sports players', 'Tailors and dressmakers', 'Textile process operatives', 'Travel agency managers and proprietors', 'Vehicle and parts salespersons and advisers', 'Water and sewerage plant operatives', and 'Window cleaners'.