Random sampling:

In this case, a sample of people is selected at random, meaning that every section of the population has an equal chance of being selected. There are, though, problems with this. For example, the researcher cannot be sure that a random sample will be representative, although it is possible to calculate statistically the level of risk involved in this method and adjust your results accordingly. It is also necessary to consider carefully whether the method of selecting the population from which the random sample is selected, is in itself valid - for example, a population comprised of the people whose names appear in a telephone directory is not the same as the population of an area as a whole.