مقایسهٔ روش‌ها

	نمونه‌گیری نظری مبتنی بر میدان	نمونه‌گیری حداکثر تنوع	نمونه‌گیری گلوله‌برفی
حوزه	روش‌شناسی پیمایش	روش‌شناسی پیمایش	روش‌شناسی پیمایش
خانواده	Process / pipeline	Process / pipeline	Process / pipeline
سال پیدایش	1967	1985 (Lincoln & Guba); elaborated 1990–2002 (Patton)	1961
پدیدآور	Barney G. Glaser and Anselm L. Strauss	Lincoln & Guba; systematised by Michael Quinn Patton	Leo A. Goodman
نوع	Qualitative iterative sampling strategy	Purposive qualitative sampling strategy	Non-probability sampling technique
منبع بنیادین	Glaser, B. G., & Strauss, A. L. (1967). The Discovery of Grounded Theory: Strategies for Qualitative Research. Aldine. ISBN: 978-0202302607	Patton, M. Q. (2002). Qualitative Research and Evaluation Methods (3rd ed.). Sage. Chapter 5: Purposeful Sampling. ISBN: 978-0761919711	Goodman, L. A. (1961). Snowball sampling. Annals of Mathematical Statistics, 32(1), 148–170.
نام‌های دیگر	field theoretical sampling, in-situ theoretical sampling, fieldwork-driven theoretical sampling, grounded field sampling	maximum variation sampling, maximum diversity sampling, MVS, heterogeneous sampling	chain-referral sampling, network sampling, respondent-driven sampling, referral sampling
مرتبط	3	5	3
خلاصه	Field-based theoretical sampling is an iterative qualitative sampling strategy in which decisions about whom to observe or interview next are made during active fieldwork, guided by emerging theoretical insights from the data already collected. Rooted in Glaser and Strauss's grounded theory, it extends theoretical sampling into naturalistic, in-situ field settings — ethnographic sites, clinical environments, organizational contexts — where data collection and analysis proceed simultaneously.	Maximum variation sampling is a purposive qualitative sampling strategy in which the researcher deliberately selects cases that span the widest possible range of variation on dimensions central to the study. The goal is not statistical representation but the identification of common patterns that cut across diverse cases as well as the documentation of the unique ways each context shapes the phenomenon under investigation.	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.