So sánh phương pháp

	Lấy mẫu trường hợp lệch dựa trên thực địa	Lấy mẫu chuỗi giới thiệu – Lấy mẫu quả cầu tuyết
Lĩnh vực	Phương pháp luận khảo sát	Phương pháp luận khảo sát
Họ	Process / pipeline	Process / pipeline
Năm ra đời	1980s–1990s (purposive/deviant case sampling literature)	1961
Người khởi xướng	Michael Quinn Patton; Yvonna Lincoln & Egon Guba	Leo A. Goodman
Loại	Purposive qualitative sampling strategy	Non-probability sampling technique
Công trình gốc	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.
Tên gọi khác	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
Liên quan	5	3
Tóm tắt	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.