مقایسهٔ روش‌ها

	نمونه‌گیری گلوله برفی مبتنی بر میدان	نمونه‌گیری هدفمند	نمونه‌گیری گلوله‌برفی
حوزه	روش‌شناسی پیمایش	روش‌شناسی پیمایش	روش‌شناسی پیمایش
خانواده	Process / pipeline	Process / pipeline	Process / pipeline
سال پیدایش	1961 (foundational); field variant developed through 1970s–1980s ethnographic and hidden population research	Formalized ~1980–1990	1961
پدیدآور	Leo A. Goodman (snowball sampling); field adaptation through ethnographic and social network research traditions	Michael Quinn Patton (systematic articulation); roots in early qualitative inquiry	Leo A. Goodman
نوع	Non-probability sampling technique	Non-probability sampling strategy	Non-probability sampling technique
منبع بنیادین	Goodman, L. A. (1961). Snowball sampling. Annals of Mathematical Statistics, 32(1), 148–170.	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.
نام‌های دیگر	in-person snowball sampling, fieldwork chain-referral sampling, field snowball sampling, face-to-face referral sampling	judgmental sampling, selective sampling, criterion-based sampling, purposeful sampling	chain-referral sampling, network sampling, respondent-driven sampling, referral sampling
مرتبط	3	4	3
خلاصه	Field-based snowball sampling is a non-probability chain-referral technique in which an initial set of in-person contacts (seeds) recruit further participants from within their real-world social networks, expanding the sample iteratively through face-to-face interaction in naturalistic field settings. It is the default snowball approach in ethnographic and community fieldwork, and is particularly valuable when the target population is hidden, hard-to-reach, or lacks a sampling frame.	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.