Production Statistics- Ready- mix Concrete

Target Population: All ready-mixed concrete producing activity units in New Zealand. Producers are separated into regions according to current local government regional boundaries. Population Covered: The survey is full coverage of the target population. Statistical Unit: Activity Unit Selection Unit: Activity Unit Collection Unit: Activity Unit Population and Sample Size: The population is about 120 geographic units. Changes in the September 2018 quarter Seasonally adjusted and trend series were introduced in the September 2018 quarter, along with new time series. Seasonally adjusted series Seasonal adjustment removes the estimated impact of regular seasonal events, such as summer holidays and pre-Christmas purchasing, from statistical series. This makes figures for adjacent periods more comparable. We recalculate the seasonally adjusted series quarterly when each new quarter's data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest quarters. We use the X-13ARIMA-SEATS seasonal adjustment program, developed in the U.S, Census Bureau, to produce the seasonally adjusted and trend estimates. Trading day adjustments An aim of time series analysis is to identify movements that are due to actual changes. Seasonal adjustment is done to remove systematic calendar-related variation. Specific adjustments can be made to remove variations due to trading day differences, which are not accounted for in a standard seasonal adjustment. We quantify and remove trading day effects when they are estimated to be statistically significant. Trend series Trend calculation removes the estimated impact of regular seasonal events and irregular short-term variation from statistical series. This reveals turning points and the underlying direction of movement over time. We recalculate trend series quarterly when each new quarter's data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest quarters. Revisions can be large if values are initially treated as outliers but are later found to be part of the underlying trend. We use the X-13ARIMA-SEATS seasonal adjustment program to produce the seasonally adjusted and trend estimates. Irregular short-term variation is removed by smoothing the seasonally adjusted series using optimal weighted moving averages. Seasonal adjustment at Statistics New Zealand has more information. en-NZ