The purpose of sampling in sociology is generally to ensure that the subjects of the research are representative of a larger group (the target population) and therefore the results can be generalised. Although random sampling is seen as a representative method, there are some research topics where researchers want to be careful that particular social groups are well-represented, perhaps in relation to social class, gender balance or ethnicity. The two main methods used for achieving this are stratified sampling and quota sampling. They are similar but quota sampling does not have the element of random selection that is present in stratified sampling and is therefore considered less reliable. It might be used in market research, for example, when field researchers are told to stop and survey 100 women (for example).