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	Fältbaserad stickprovsuttagning av avvikande fall	Snöbollsurval
Ämnesområde	Surveymetodik	Surveymetodik
Familj	Process / pipeline	Process / pipeline
Ursprungsår	1980s–1990s (purposive/deviant case sampling literature)	1961
Upphovsperson	Michael Quinn Patton; Yvonna Lincoln & Egon Guba	Leo A. Goodman
Typ	Purposive qualitative sampling strategy	Non-probability sampling technique
Ursprungskälla	Patton, M. Q. (2002). Qualitative Research and Evaluation Methods (3rd ed.). Sage Publications. ISBN: 978-0761919711	Goodman, L. A. (1961). Snowball sampling. Annals of Mathematical Statistics, 32(1), 148–170.
Alias	field deviant case sampling, outlier case sampling in field research, extreme case sampling in fieldwork, in-situ deviant case sampling	chain-referral sampling, network sampling, respondent-driven sampling, referral sampling
Närliggande	5	3
Sammanfattning	Field-based deviant case sampling is a purposive strategy that deliberately selects cases deviating markedly from an established pattern or norm, with data collected through direct fieldwork — observation, in-situ interviews, and ethnographic engagement — in the participants' natural settings. By studying outliers on-site, researchers gain contextually grounded insight into why and how certain cases diverge from the typical pattern.	Snowball sampling is a non-probability recruitment technique in which initial participants (seeds) refer the researcher to others who meet the study criteria, and those referrals in turn refer further participants. The sample grows incrementally — like a rolling snowball — until the required size or theoretical saturation is reached. It is the method of choice when a target population has no accessible sampling frame, such as undocumented migrants, illicit drug users, survivors of stigmatised experiences, or members of closed professional networks.