Non-Random Sampling

In non-random sampling the units are not chosen by chance, so not every unit has an equal chance of being selected; instead the convenience or judgement of the investigator decides who is included.

Suppose you must pick 10 out of 100 households in a locality and you choose the ones conveniently located, or those known to you or a friend. Here you are using your own judgement — that is, introducing bias — so the selection is not random. …