The index is still being built. It needs 8 weeks of our own price records before we state how prices are changing.
How it is worked out
The average asking price moves when the mix of cars for sale moves, for example when more new, expensive models are listed. This index compares like with like instead.
Cars are grouped by model, build year (in bands of 3 years) and kilometres. For each week, we take the median asking price of each group from the prices we recorded for cars for sale that week. We compare a week with the one before using only the groups that have 3 or more cars in both weeks, weighting each group by its number of cars the week before. The week-on-week movement is chained onto the index, which is 100 in the first full week.
The figures are medians of groups of cars, never single listings, and cover only prices we have recorded ourselves. Weeks start on Monday, New Zealand time. Changes are shown once 8 weeks of index exist.
The index is updated each Monday for the week before.