Monthly Weighted Median CPI MoM

Monthly Weighted Median CPI MoM is a trend inflation measure from the ABS, Australia's national statistical agency. It sits in the 17th Consumer Price Index, or CPI. It tracks the prices of goods and services bought by metropolitan households in 8 capital cities, nationally. The basket holds 11 groups and 87 expenditure classes, or ECs, with weights updated each January. It reports the month-on-month change at the 50th percentile after seasonal adjustment, alongside the trimmed mean.

Monthly items are priced each month, quarterly items in the same month each quarter, and annual items once a year. Months with no new price get carry forward imputation. Results come around 4 weeks after month end at 11:30am Sydney time, except November data appears in January. Publication began October 26, 2022, backcast to September 2017.

Each release shows headline All groups inflation, the 11 groups, and trend series such as trimmed mean and weighted median. Volatile items are fruit and vegetables plus automotive fuel. Earlier months are revised as fuller data arrives, as monthly measurement spreads, or as seasonal factors are re-estimated. Month-on-month moves stay volatile, so the same month a year earlier or the 3 months before suit trends.

The middle class of all 87 moves the median, not the extremes.

• Housing: captures rents, new dwellings excluding land, electricity, gas and other household fuels.
• Food and non-alcoholic beverages: captures bread and cereals, meat and seafood, dairy, fruit and vegetables, other food, drinks and meals out.
• Transport, Recreation and culture: captures automotive fuel, motor vehicles, maintenance and fares, holiday travel and accommodation, and audio-visual and sporting goods.
• Alcohol and tobacco, Insurance and financial services: captures alcohol, tobacco, insurance premia and financial services, with tobacco and insurance often rising strongly.
• Clothing and footwear, Communication: captures garments, footwear, telecom equipment and services, with seasonal sales.
• Furnishings, household equipment and services, Health, Education: captures furniture, appliances, household services and medical costs, plus yearly school fees, and usually stays steady.

January 2024 was released February 28, 2024 at 3.4% annual headline, as in December and down from 4.3% in November. Annual trimmed mean was 3.8%, and the index excluding volatile items and holiday travel was 4.1%.

Automotive fuel fell 0.9% in the month but still rose 3.1% over the year. Holiday travel fell 5.2% in the month. Gas fell 1.4% on a base effect, while electricity rose 0.8% with rebates and 15.3% without them.

Rents held at 7.4% while new dwellings eased to 4.8%. Headline can stand still while tails swing.

1. Concurrent seasonal adjustment: Adjust seasonal classes with factors re-estimated monthly from all data to date; other classes enter unadjusted.
2. Relative weight: Compute each class change from its two latest seasonally adjusted indexes. Give each class its previous month share of All groups monthly CPI. Yearly weights use spending surveys or national accounts.
3. Ranking: Rank classes from lowest to highest change and cumulate weights to 100%. The median is the change of the first class at or just over 50%. The trimmed mean averages the middle 70% between 15% and 85%, partly counting classes that cross.
4. Percentage change: Build All groups, trimmed mean and median from the classes. Take the index point change over the previous index times 100. Use indexes rounded to one decimal place, then round rates to one decimal place. For example, 114.2 less 113.5 is 0.7 points, and 0.7 over 113.5 times 100 is 0.6%.
5. Worked example: Five illustrative classes move by minus 2.0% and 0.1%, 0.4%, 0.9% and 5.0%, with weights 10, 30, 25, 20 and 15. Cumulated weights reach 10%, 40%, 65%, 85% and 100%, so the median is 0.4% despite the extremes.