Saturation is the point in qualitative data collection at which further cases are held to be adding nothing new — the categories are filled out and additional interviews yield no fresh properties. The idea comes from grounded theory, where it was tied to a specific programme of theoretical sampling, and it has since been detached from that programme and used loosely as a justification for stopping. That detachment is disputed. Some writers argue saturation is inseparable from the analytic approach that produced it, others that it can never be demonstrated but only asserted, others still propose counts or criteria for declaring it. There is no agreed test and no body that could impose one.
Why this entry carries no source list. This lexicon cites an official primary source wherever one exists, and says so plainly where none does. No body governs this term. There is no standards organisation for it, no register, and no text whose authors could claim to have settled its meaning. Methods literature describes practice and argues about it; a citation to one author would dress a position in a live argument as a rule, which would mislead more than silence does. What follows is the convention as it is actually used, with the disagreements named rather than smoothed over.