Saturation point
The saturation point is the moment in a qualitative study when further data collection stops adding new themes or insights, so the researcher can stop recruiting. It is where data saturation is judged to have been reached.
How it works
Researchers identify the saturation point by tracking what each new interview adds. A common approach lists the themes found after each interview, or each small group of interviews, and watches the count of new ones fall. When a run of interviews adds almost nothing, and nothing that would change the findings, the point has been reached.
Where the point falls depends on the population and the question: a narrow question with similar participants saturates sooner than a broad question across diverse segments. A simulation study published in PLOS ONE showed how strongly the likelihood of observing every theme depends on how common each theme is. Many teams therefore plan for saturation within each segment separately.
A worked example
An energy company interviews two customer segments about switching supplier. Among 9 renters, the last new theme appears at interview 7. Among homeowners, new themes keep appearing until interview 14, because installations, solar panels and home moves each raise their own issues.
Related
Automate this in Pulse
Reading each Pulse transcript as it arrives lets a researcher notice the interview after which no new theme appears, and stop recruiting there.