So sánh phương pháp

	Lấy mẫu lý thuyết thử nghiệm	Chọn mẫu có chủ đích	Lấy mẫu chuỗi giới thiệu – Lấy mẫu quả cầu tuyết
Lĩnh vực	Phương pháp luận khảo sát	Phương pháp luận khảo sát	Phương pháp luận khảo sát
Họ	Process / pipeline	Process / pipeline	Process / pipeline
Năm ra đời	1967 (theoretical sampling origin); compound practice formalized in qualitative methodology literature	Formalized ~1980–1990	1961
Người khởi xướng	Glaser & Strauss (theoretical sampling); pilot study concept is longstanding in research methodology	Michael Quinn Patton (systematic articulation); roots in early qualitative inquiry	Leo A. Goodman
Loại	Qualitative sampling strategy with pilot phase	Non-probability sampling strategy	Non-probability sampling technique
Công trình gốc	Glaser, B. G., & Strauss, A. L. (1967). The Discovery of Grounded Theory: Strategies for Qualitative Research. Aldine. ISBN: 978-0202302607	Patton, M. Q. (1990). Qualitative Evaluation and Research Methods (2nd ed.). Sage. ISBN: 978-0803937796	Goodman, L. A. (1961). Snowball sampling. Annals of Mathematical Statistics, 32(1), 148–170.
Tên gọi khác	pilot-phase theoretical sampling, exploratory theoretical sampling, preliminary theoretical sampling	judgmental sampling, selective sampling, criterion-based sampling, purposeful sampling	chain-referral sampling, network sampling, respondent-driven sampling, referral sampling
Liên quan	3	4	3
Tóm tắt	Pilot theoretical sampling applies the logic of theoretical sampling — selecting participants based on emerging concepts and theory — within a deliberate pilot or preliminary phase of a study. Rather than committing immediately to a full sampling strategy, the researcher conducts a small initial round of data collection and analysis to test whether theoretical sampling is feasible, to refine the sensitizing concepts guiding participant selection, and to identify whether the field is productive before full-scale data collection begins.	Purposive sampling is a non-probability strategy in which the researcher deliberately selects participants, documents, or cases that are information-rich with respect to the research question. Rather than drawing units at random, the researcher applies explicit criteria aligned with the study's purpose, maximising the depth and relevance of the data collected. It is the default sampling logic in most qualitative research designs and is also used in mixed-methods and applied evaluative work.	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.