The Federal Budget papers contain a number of charts, tables and forecasts. The forecasts are the part most people focus on. They are also the part most likely to be misunderstood.
When the Reserve Bank publishes a forecast, it is trying to predict the economy. The Bank looks at the data, consults its models, applies its judgement, and prints a number it thinks is most likely to happen. When the budget papers publish a forecast, they are doing something very different. They start with where the economy is today and assume it returns to something like normal over the medium term. The forecast then asks a simple costing question. Under normal conditions in the out years, what would revenue and expenses look like?
The distinction matters. The budget forecasts are not predictions. They are an arithmetic exercise built on top of an assumed normal economic equilibrium. The numbers that define that equilibrium, things like the medium-term GDP growth rate, the wage and price assumptions, the unemployment anchor, are framework conventions. They are not Treasury's literal central case for the economy. If the equilibrium is wrong, every number that flows from it is wrong too.
This year's papers contain an equilibrium that does not add up.
The reversion always looks the same
Start with real GDP. The black line is what actually happened. The orange lines are successive Treasury forecasts. Almost every forecast bends back toward 2.5 to 3 per cent growth, regardless of where the economy actually is.