Tax records are used to identify people who received income from a business in an industry relating to one of the trades. Information about occupation is not available in IRD records so we use only industry to identify people. We use the same core industries for the census data.
The workforce in a sector consists of those who earned income from businesses in industries relevant to each trade sector. An individual is included as an employee in a particular quarter if they received at least $1500 in wages or salary for that quarter. An employer is included in a particular tax year if they received any income from a business that year. Employer data is not available on a quarterly basis. Yearly numbers are calculated as averages of the quarters.