We have been warning of the problems inside China’s official production data for the last 3 or 4 years. But here’s further proof of the “wackiness” of the numbers that come out of China’s National Bureau of Statistics and the China Nonferrous Industry Association.

Aluminium smelting is a steady-state process. There are no moving parts like in a widget factory. Electricity and alumina are poured into a bath and pure aluminium forms on the bottom of the bath. The only batch part of the process is that the workers remove the metal from the bottom of the bath on a cyclic basis, tapping each pot in turn.

So a normal operation will turn out roughly the same amount of metal per day. Multiply that by 130 for the number of smelters in China, and you can get a pretty good gauge of how much metal is going to be produced. The only major corrections to that are if a potline is idled, or if a line is started up. And a start up is usually a slow process over several months, while a closure can be in hours (but only by accident - no plant would willingly allow hundreds of pots to freeze over all at once.)

This chart shows the % change in the daily run rate from month to month.

I am no statistician, but this pattern makes no sense. In particular, 2013 seems to be a time for turning up the “crazy dial”. So far this year, we have had minus 10%, plus 8.8%, minus 9.4%, a couple of quiet months, then plus 7.8% followed by minus 3.4%.

In the period shown in the chart, China’s aluminium production has grown from 45,000t per day to 60,000 tonnes per day, so a growth of 33% in 3 and a half years. But clearly, if you believe the data published by China’s authorities, it has been a case of the “Chinese Waltz” - where the dance moves are chosen randomly.

And this is just the reported production. There’s another 10% of China’s aluminium production doesn’t even get into the official numbers.