We take apprentices first enrollment into apprenticeship (level 4, 100+ credit) course (trade defined by MOE derived occupation). From these apprentices, we calculate the time between their start and end date as their completion duration.
Yearly income of apprentices is tracked from IRD tax records, taking income earned from construction businesses only. Monthly income is adjusted for months not worked. Real measures are adjusted to 2020Q1 based on wage inflation.
Income is average between groups fitting under different cut offs based on completion duration.