today. Large animals now extinct provided more meat than the animals which we are familiar with. Some parts of the continent were richer in vegetable food, but there were no cultivated crops or animals that could be domesticated such as cattle and sheep. As Australia was isolated from the rest of the world, Aboriginals had very little contact with other people from whom to borrow tehniques, to trade good, to acquire crop seeds or animals. Each clan grouping occupied a welldefined area of land. The group belonged with, or to the land as well the animals and plants. They had no idea of being able to buy or sell land, the land was given long ago, in the Dreamtime. Aborigines were limited to the food, which they had growing naturally in their area. But they knew when, where and how to find anything edible. But food was not obtained without effort. Inland, the search for water was a life and death matter. Aborigines survived where the others would have died
For instance, in countries like Denmark and The Netherlands the national statistical agency has access to the population registry (see also Bethlehem Chapter 26). This makes it possible for the national statistical agency to draw a probability sample not only of the general population, but also to draw specific subsamples. Some countries have good lists of mobile phone users, whereas others do not. In some areas, the telephone system has a welldefined structure of used and unused number banks, which makes it possible to generate random telephone numbers with good coverage properties. In most areas, the telephone system does not have such a structure or several competing telephone systems are in use, which makes generating random telephone numbers more difficult (cf. Steeh, Chapter 12). Web surveys are a special challenge to survey methodologists, because the coverage problem is large and difficult to solve
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