1913-1947, excluding 1919: unemployment rates are expressed as a percentage of the insured unemployed to all insured persons.

1948-1968: the unemployment rate is expressed as the number of people registered as unemployed at employment exchanges and associated offices as a percentage of the total of those unemployed plus the number of employees in employment.

1969-1971: the unemployment rate is expressed as the number of registered unemployed as a percentage of the total of employees and unemployed.

1972-1982: the unemployment rate is expressed as the number of registered unemployed aged 18 and over as a percentage of the workforce (that is, of employees in employment, the self-employed, the unemployed, HM Forces and people on work-related government training programmes).

1983-April 1998: the unemployment rate is expressed as the number of persons aged 18 and over claiming unemployment-related benefits as a percentage of the workforce.

Source: 1993b