Some authors extend the typology of non-probabilistic samples, which they consider suitable for qualitative research. They are as follows:

▸ Various samples or of maximum variation. Its aim is to show different perspectives of the phenomenon studied.

▸ Homogeneous samples (people with the same level of education).

▸ Snowball sampling (samples are selected based on the above).

▸ Sample of extreme cases (for example, extremely violent people).

▸ Samples for opportunity or convenience (presented to the researcher at a time, or is the most accessible).

▸ Theoretical or conceptual samples (selected cases to test these theories).

▸ Confirmatory samples (when in the analyzed cases some controversy arises, doubt… and more cases of different type are chosen to confirm or not).

▸ Samples of extremely important cases (for example, testimony of survivors of a shipwreck, or of newspaper editors who have faced extremely serious cases, for example the one represented on the so-called "Pentagon papers" by the Washington Post).

▸ Intentional, directed or reasoned sample: the person selects the sample trying to be representative, but according to his intention or opinion.

▸ Erratic or circumstantial sample: selection of cases arbitrarily (see “fortuitous or accidental” sample).