Where individuals are chosen for the sample in an accidental way, ie entirely by chance, and have an equal chance of being selected (in the same way that each of the balls of the National Lottery has an equal chance of coming out first). The main criticism of non-random sampling is the fact that because an element of judgment is introduced in the process, with the interviewer being able to choose who they want to include in the sample, not everyone has an equal chance of being selected, therefore, samples will be biased. Random sampling methods consist of simple random, systematic, stratified and cluster sampling.