ONE of the problems facing a manager trying to convince colleagues to attack the China market is getting the data to build a case for investment. Economic data in China can be hard to come by. Even the population figures can be suspect. Although officially 1.1 billion, some have estimated the figure to be as high as 1.5 billion, which would make a nasty dent in the gross national product per head figure usually used as a measure of development. So it is good news to hear that the Ministry of Posts and Telecommunications has decided to send data to US telecommunications firm American Telephone and Telegraph (AT&T) for its popular reference book The World's Telephones. Although figures on China's use of telephones are quoted widely, they seem to change every time they appear. The ministry told AT&T it had 8.5 million access lines. If one accepts the 1.1 billion figure, this gives one line for every 130 people. This compares with Hongkong's figure of one for every 1.6 people. The problem is, it is not easy to believe the figures China has supplied. AT&T's announcement quotes the ministry as saying the number of lines increased by 24 per cent in 1991. But in the past two months alone, the China Daily has quoted at least two other figures for lines per head. Like the population figures, there is little incentive to get the data right, especially if it makes the economic miracle look a little less miraculous. But just like the population figures, there may be a more mundane explanation. As the central planning system withers away, collecting data across that giant land mass becomes ever more difficult.