When AFR Weekend asked Glasenberg this week about whether he felt vindicated, he said that "with hindsight we were proved correct.

"What I said at the time is, China is hard to read on a short-term basis. You never know what lever they are going to pull from one day to the next," he said.

Take the iron ore price as an example of why no one trusts the short term. It's risen 23 per cent since the start of the February, but a spate of data has shown China's steel sector is in deep trouble, and iron ore stockpiles are reportedly rising. In short, everything suggests that iron ore should be falling.

Belief in China claim

Glasenberg made it clear at Glencore's annual results that he has "always believed in China in the long-term".

China Caixin Manufacturing PMI and iron ore price

But if he and his peers are struggling to read China right now, who can?

For the chief executive of one of the world's biggest exporters of iron ore to China, Fortescue Metals Group, Nev Power, "it is about reading the economic policies and understanding what implications they have for the market.


"That's where the reading part comes in – the rest of it is about responding to the market. We talk very closely with our customers to understand what their order books look like so we can make our estimates."

But he can't resist a thinly veiled swipe at rivals BHP Billiton and Rio Tinto. "I note that a little while back there were people saying they had better analysts or had been there longer or they somehow had better insights into China."

Much has been made of the "peak steel" production forecasts put forward by Rio and BHP.

BHP is tipping a peak of 935 to 985 million tonnes around 2025, while Rio tips about 1 billion tonnes towards 2030. But some Chinese observers believe peak steel may have already passed.

It remains to be seen if the two majors are right, but Power and Fortescue aren't getting stuck on any one number.

Estimating is 'fraught with danger'

"There have been people in the industry predicting steel demand, which has been a gross overstatement of where we have ended up, so I think it is quite fraught with danger to try and estimate that too closely. Our strategy is to respond to the market".

Of course, that can be tough when every fresh round of data on China adds to fears of a slowdown.


But Fortescue independent director and former Australian ambassador to China, Geoff Raby, says it's important not to panic.

"There is a growth industry in Chinese pessimism out there at present – a lot of it is lack of experience, a lot of it is just market analysts chasing each other in circles.

"It is hilarious how you get a 2 percentage point change in a growth number or any indicator – plus or minus – and markets start gyrating wildly. As if those numbers have that level of scientific precision.They don't."

He argues every economy can be difficult to call, particularly in the current climate, because "most people have no idea and there is no consensus.

"Even an economy as open as the United States', where everything is out there including the Federal Reserve's board minutes, people really don't know where that is."

China, of course, is much more opaque. But Raby, who is seen as one of the most knowledgeable players in the mining industry on China, is convinced it's not impossible to understand.

No more difficult to read

"With the right experience and exposure to the economy, and a broad perspective – with a sense of how things have changed over time – China is not much more difficult than anywhere else to call," Raby says.


"A lot of people have [been able to read it] for a long time. I certainly wouldn't say it's impossible to read, you've got enough data available."

BHP spinoff South32 doesn't put anywhere near the resources into reading China as BHP and Rio do, in large part because it is not nearly as dependent on China as them, or as big.

Chief executive Graham Kerr said the miner "can get broad-brush approaches" on China.

"We are no better than anyone else [at reading it], we protect ourselves by managing our business to operate in a low price environment."

But Kerr also underlines the other big problem with understanding the Chinese market: "you run into the challenge of 'how good are statistics in China?' "

There have long been fears that the headline numbers released by authorities are manipulated.

Famously, GDP numbers keep coming in within 0.1 per cent of predictions. GDP growth this year was 6.9 per cent, against government expectations of 7 per cent, and compared with 7.3 per cent in 2014.

Relatively relaxed


Raby is relatively relaxed about the data.

"In terms of aggregate growth rate, China is pretty much where the government intended it to be – you could say that is just a trick of the numbers," Raby says.

"But if you look at other indicators – growth in consumption, recovery in the property market – they are consistent with an economy somewhere in the order of where the government says it is today."

Given the uncertainty about China's numbers, Raby warns it is important not to do a basis point change comparison – up or down – on the previous month.

Instead, the numbers can be useful to measure performance over time – to look at trends that are broadly consistent across the economy.

"It doesn't mean that the numbers themselves don't have a lot of inherent problems, so that's why the best you can do with them is treat them as reasonable indicators of broad orders of magnitude. That's all you need really."

Proxies, like energy consumption and transport data, are useful to test data but they don't prove anything in and of themselves, Raby says.

"But I think a lot of analysts now for some reason believe the proxies prove more than the aggregate GDP number."


Growth 'the big story'

Raby says this year, GDP should be north of 6 per cent, but "it is not the number so much, it is: what does it mean? The world's second-biggest economy growing at a speed that will see per capita incomes double in a bit over a decade. That is the big story."

The Chinese government will set a new GDP growth target at the National People's Congress. It is expected to be between 6.5 and 7 per cent – that would be the first time the government has not set a specific number.

Top-line economic growth is important, but for the miners, what is just as crucial is its composition.

The shift from an economy heavily reliant on industrial production to a more service-oriented one has occurred more quickly than anticipated by most, including BHP's Mackenzie.

"In the near term, as industrial overcapacity is reduced, this will further constrain demand for commodities, and these near-term changes have been amplified by disruption to the oil market and broader global uncertainty," Mackenzie says.

"Both have affected sentiment and further increased the volatility of commodity prices, which we expect will continue in the short to medium term."

China is a riddle


Mackenzie might be downbeat on the shorter-term outlook for China.

And there is no doubt China is a riddle. But most of the big mining bosses – from Mackenzie, to Walsh, to Glasenberg – are more upbeat on where China is heading longer term.

Maybe the last word should go to Ivan.

"I have always believed in China in the long term, I believe in their consumption of commodities in the long term, whether you move more from an infrastructure-type environment to a consumer environment, it's still very good for the commodities we produce.

"Long term, I believe China is going to be very good for consumption of commodities and I keep stating that."

But with China, there is always a caveat.

"Let's see what they are going to do from one day to the next."