Sampling is easy to establish in quantitative research designs. The sampling frame can easily be extracted once the population universe is established and the appropriate sampling formula is identified. However, qualitative research is not as lucky. Establishing the sample and the sampling process in qualitative inquiry is almost often a subject of contention, and takes much more time in persuading panel members during research defense sessions. A systematic sampling process in qualitative research designs is rarely established. Often, what is used is a very arbitrary and uninformed purposive sampling technique (sample identified on purpose). It is indeed difficult, but should not be impossible.
The snowballing sampling technique is a systematic non-probabilistic purposive sampling method that is very apt for qualitative research. Highly qualitative and exploratory studies call for a purposive non-probability sampling design, which is not after the representativeness of samples. A purposive non-probability sampling design relies heavily on the availability of respondents, especially those who are difficult to locate for interviews.
A snowballing sampling technique can be employed to seek out informants or respondents, who are otherwise difficult to locate and identify. The snowballing sampling method is akin to the opportunity sampling technique, the chaining sampling technique and the referral sampling technique (referred informants). The works of Dr. Earl Babbie, Dr. Fely David, Dr. Roberto Padua, Dr. David Garson and Dr. Wilfredo Arce have all provided the foundational, philosophical and procedural bases in employing the abovementioned sampling techniques.
The snowballing sampling technique is most proper when the members of the target respondents are difficult to locate. A snowball is the process of accumulation of referrals as each located and interviewed informant suggests other informants whom they happen to know and locate. For Arce, it “results from one key informant being interviewed and asked for suggestions on who else might be good informants, and the next informant is chosen on the basis of this suggestion.” As an opportunity sampling technique, the informants were selected and interviewed mainly because they were located and made available for and in a particular study. David used accidental non-probability sampling technique as a derivative of the opportunity sampling technique. In accidental sampling technique, the respondents were chosen as they become available. This technique resembled that of Garson’s chain sampling method, where the aim is to “obtain a saturation of informants….to reveal common cultural understanding....in a chaining process.”
The question is: when does the sampling process of snowballing, chaining, referring and opportunity-seeking stop?
Simple! It stops when the so-called saturation sample is spotted. A saturation sample is a point of sampling where new respondents are now unable to give new information that generally depart from those given by previous respondents. A saturation respondent or informant does not give new data-value, thus this is the signal that getting new samples is not anymore necessary.
Amorado, Ronnie V. 2007. Fixing Society: The Inside World of Fixers in the Philippines. Davao City: Ateneo de Davao University - Research and Publication Office.
Amorado, Ronald V. 2005. Fixing Society: The Inside World of Fixers in the Philippines. A Doctoral Dissertation. Davao City, Philippines: Ateneo de Davao University-Graduate School of Arts and Sciences.
Arce, Wilfredo F. 2001. Systematic Qualitative Data Research: An Introduction for Filipino Practitioners (2nd ed). Quezon City: Ateneo de Manila University – Office of Research and Publications.
Babbie, Earl. 1998. The Practice of Social Research (8th ed). Wadsworth: Thomson Learning Inc.
David, Fely P. 2002. Understanding and Doing Research: A Handbook for Beginners. Iloilo City: Central Philippine University – Social Science Research Institute.
Garson, G. David. 2004. “Ethnographic Research.” Course Syllabus on Ethnographic Research. North Carolina State University. Raleigh, North Carolina.
Padua, Roberto N. 2000. Elements of Research and Statistical Models. Cagayan de Oro City: MPSC Publishing House. USA: Wadsworth Publishing Company.