Snowball sampling

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In sociology and statistics research, snowball sampling [1] (or chain sampling, chain-referral sampling, referral sampling [2] [3] ) is a nonprobability sampling technique where existing study subjects recruit future subjects from among their acquaintances. Thus the sample group is said to grow like a rolling snowball. As the sample builds up, enough data are gathered to be useful for research. This sampling technique is often used in hidden populations, such as drug users or sex workers, which are difficult for researchers to access. As sample members are not selected from a sampling frame, snowball samples are subject to numerous biases. For example, people who have many friends are more likely to be recruited into the sample. When virtual social networks are used, then this technique is called virtual snowball sampling. [4]

Contents

It was widely believed that it was impossible to make unbiased estimates from snowball samples, but a variation of snowball sampling called respondent-driven sampling [5] [6] [7] has been shown to allow researchers to make asymptotically unbiased estimates from snowball samples under certain conditions. Snowball sampling and respondent-driven sampling also allows researchers to make estimates about the social network connecting the hidden population.

Description

Snowball sampling uses a small pool of initial informants to nominate, through their social networks, other participants who meet the eligibility criteria and could potentially contribute to a specific study. The term "snowball sampling" reflects an analogy to a snowball increasing in size as it rolls downhill. [8]

Method

  1. Draft a participation program (likely to be subject to change, but indicative).
  2. Approach stakeholders and ask for contacts.
  3. Gain contacts and ask them to participate.
  4. Community issues groups may emerge that can be included in the participation program.
  5. Continue the snowballing with contacts to gain more stakeholders if necessary.
  6. Ensure a diversity of contacts by widening the profile of persons involved in the snowballing exercise.

Applications

Requirement

The participants are likely to know others who share the characteristics that make them eligible for inclusion in the study. [9]

Applicable situation

Snowball sampling is quite suitable to use when members of a population are hidden and difficult to locate (e.g. samples of the homeless or users of illegal drugs) and these members are closely connected (e.g. organized crime, sharing similar interests, involvement in the same groups that are relevant to the project at hand). [9]

Application field

Social computing

Snowball sampling can be perceived as an evaluation sampling in the social computing field. For example, in the interview phase, snowball sampling can be used to reach hard-to-reach populations. Participants or informants with whom contact has already been made can use their social networks to refer the researcher to other people who could potentially participate in or contribute to the study.

Conflict environments

It has been observed that conducting research in conflict environments is challenging due to mistrust and suspicion. A conflict environment is one in which people or groups think that their needs and goal are contradictory to the goals and or needs of other people or groups. These conflicts among people or groups might include claims to territory, resources, trade, civil and religious rights that cause considerable misunderstanding and heighten disagreements, leading to an environment with lack of trust and suspicion. In a conflict environment, the entire population (rather than a specific group of people) is marginalized to some extent, which makes it hard for investigators to reach potential participants for their research. For example, a threatening political environment under an authoritarian regime creates obstacles for the investigators to conduct the research. Snowball sampling has been demonstrated as a useful method in conducting research in conflict environments, such as in the context of the Israel and Arab Conflict. [10] Snowball sampling allows the investigators to approach the marginalized population at cognitive and emotional level and enroll them in study. Snowball sampling addresses the conditions of lack of trust that arises due to uncertainty about the future through trace-linking methodology. [11]

Expert information collection

Snowball sampling can be used to identify experts in a certain field such as medicine, manufacturing processes, or customer relation methods, and gather professional and valuable knowledge.

For instance, 3M called in specialists from all fields that related to how a surgical drape could be applied to the body using snowball sampling. Every involved expert can suggest another expert who they may know could offer more information.

Public and population health research with marginalized and stigmatized populations

Snowball sampling can be used to recruit participants in research in marginalized, criminalized or other stigmatized behaviour, and its consequences. Examples include the use of illegal substances (e.g., unprescribed drugs), collection of illegal materials (e.g., ivory, unlicensed weapons), or stigmatized practices (e.g., support for anorexia, sexual fetish). Exclusion from majority society or fear of exposure or of shaming makes it difficult to contact participants through usual means. However, the nature of many of these behaviours means that people engaging in them have contact with each other. Snowball sampling is used in many studies of street-involved populations. [12]

Advantages and disadvantages

Advantages

  1. Locate hidden populations: It is possible for the surveyors to include people in the survey that they would not have known but, through the use of social network.
  2. Locating people of a specific population: There are no lists or other obvious sources for locating members of the population (e.g. the homeless, users of illegal drugs). The investigators use previous contact and communication with subjects then, the investigators are able to gain access and cooperation from new subjects. The key in gaining access and documenting the cooperation of subjects is trust. This is achieved that investigators act in good faith and establish good working relationship with the subjects.
  3. Methodology: As subjects are used to locate the hidden population, the researcher invests less money and time in sampling. Snowball sampling method does not require complex planning and the staffing required is considerably smaller in comparison to other sampling methods. [13]

Snowball sampling can be used in both alternative and complementary research methodologies. As an alternative methodology, when other research methods can not be employed, due to challenging circumstancing and when random sampling is not possible. As complementary methodology with other research methods to boost the quality and efficiency of research conduct and to minimize the sampling bias like quota sampling. [11] [14]

Disadvantages

  1. Community bias : The first participants will have a strong impact on the sample. Snowball sampling is inexact and can produce varied and inaccurate results. The method is heavily reliant on the skill of the individual conducting the actual sampling, and that individual's ability to vertically network and find an appropriate sample. To be successful it requires previous contacts within the target areas, and the ability to keep the information flow going throughout the target group. [15]
  2. Non-random: Snowball sampling contravenes many of the assumptions supporting conventional notions of random selection and representativeness. [16] However, social systems are beyond researchers' ability to recruit randomly. Snowball sampling is inevitable in social systems.
  3. Unknown sampling population size: There is no way to know the total size of the overall population. [9]
  4. Anchoring : Another disadvantage of snowball sampling is the lack of definite knowledge as to whether or not the sample is an accurate reading of the target population. By targeting only a few select people, it is not always indicative of the actual trends within the result group. Identifying the appropriate person to conduct the sampling, as well as locating the correct targets is a time-consuming process such that the benefits only slightly outweigh the costs.
  5. Lack of control over sampling method: As the subjects locate the hidden population, the research has very little control over the sampling method, which becomes mainly dependent on the original and subsequent subjects, who may add to the known sampling pool using a method outside of the researcher's control.

Compensations

The best defense against weaknesses is to begin with a set of initial informants that are as diverse as possible. [9] Efforts to improve the main disadvantage of snowball sampling resulted in the respondent-driven sampling (RDS) method. [17] RDS augments the referral method by weighting the sample in order to compensate for the initial non-random selection, which may lead to the reduction of errors occurring in sampling by the referral method. [13]

Virtual snowball sampling

Virtual snowball sampling is a variation of traditional snowball sampling and it relies on virtual networks of participants. It brings new advantages but also disadvantages for the researcher.

Advantages

Disadvantages

Example used in research

Virtual snowball sampling technique was used in order to find participants for the study of a minority group – Argentinian entrepreneurs living in Spain. About 60 percent of this population has double nationality – both Spanish and Argentinian. Spanish national statistics classifies them as European citizens only and there is no information about the place of birth tied to the profiles of entrepreneurs in Spain either. Therefore, referring to national statistics only, made it impossible to build a sample frame for this research. The use of virtual networks in this example of hard to reach population, increased the number of participating subjects and as a consequence, improved the representativeness of results of the study. [4]

Ethical issues

Ethical concerns may prevent the research staff from directly contacting many potential respondents. Therefore, program directors or personnel who knew of possible respondents can make initial contacts and then ask those who were willing to cooperate to personally contact the project. In each instance, the newly recruited research participant must be trained to understand and accept the eligibility criteria of the research. For example, in a study on treatment for substance-use disorder which used snowball sampling, it was difficult for many to understand the eligibility criteria because some criteria violated common-sense understandings concerning treatment and non-treatment. For example, many people define themselves as untreated in spite of possible long stays in civil commitment programs because their commitments to these institutions were involuntary and/or because they had become re-addicted upon release and then recovered at a later time. [18] Therefore, the quality of informed consent was in doubt.

In a qualitative research, apprehension around feelings of compulsion are reviewed for potential ethical dilemmas and recommendations for research process are made. [19]

Improvements

Snowball sampling is a recruitment method that employs research into participants' social networks to access specific populations. According to research mentioned in the paper written by Kath Browne, [20] using social networks to research is accessible. In this research, Kath Browne used social networks to research non-heterosexual women. Snowball sampling is often used because the population under investigation is hard to approachable either due to low numbers of potential participants or the sensitivity of the topic. The author indicated the recruitment technique of snowball sampling, which uses interpersonal relations and connections within people. Due to the use of social networks and interpersonal relations, snowball sampling forms how individuals act and interact in focus groups, couple interviews and interviews. As a result, snowball sampling not only results in the recruitment of particular samples, use of this technique produces participants'accounts of their lives. To help mitigate these risks, it is important to not rely on any one single method of sampling to gather data about a target sector. In order to most accurately obtain information, a company must do everything it possibly can to ensure that the sampling is controlled. Also, it is imperative that the correct personnel is used to execute the actual sampling, because one missed opportunity could skew the results.

Respondent-driven sampling

A new approach to the study of hidden populations. It is effectively used to avoid bias in snowball sampling. Respondent-driven sampling involves both a field sampling technique and custom estimation procedures that correct for the presence of homophily on attributes in the population. The respondent-driven sampling method employs a dual system of structured incentives to overcome some of the deficiencies of such samples. Like other chain-referral methods, RDS assumes that those best able to access members of hidden populations are their own peers. [21]

Peer Esteem Snowballing (PEST)

Peer Esteem Snowballing is a variation of snowball sampling, useful for investigating small populations of expert opinion. Its proponents [22] argue that it has a number of advantages relative to other snowballing techniques:

  1. reduces the selection bias inherent in initial seed samples for a snowball by advocating for a nominations phase that objectively identifies contact seeds for the first wave;
  2. by analysing network data it provides an estimate of the population size, unbiased by any researcher defined population boundary;
  3. by reporting the estimate of the sample size vis a vis the population, it provides a measure of relative significance (optimal sampling data can be reported in this context);
  4. through a network analysis of referrals it allows for identifying clusters of experts that may be instrumental in explain variations in their response profile;
  5. allows for a referrals nominations strategy that, in certain cases, could improve response rates, while the nominations strategy acts as an ultimate validation of expertise for informants and therefore improves content validity.

Related Research Articles

<span class="mw-page-title-main">Research</span> Systematic study undertaken to increase knowledge

Research is "creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of evidence to increase understanding of a topic, characterized by a particular attentiveness to controlling sources of bias and error. These activities are characterized by accounting and controlling for biases. A research project may be an expansion of past work in the field. To test the validity of instruments, procedures, or experiments, research may replicate elements of prior projects or the project as a whole.

In statistics, survey sampling describes the process of selecting a sample of elements from a target population to conduct a survey. The term "survey" may refer to many different types or techniques of observation. In survey sampling it most often involves a questionnaire used to measure the characteristics and/or attitudes of people. Different ways of contacting members of a sample once they have been selected is the subject of survey data collection. The purpose of sampling is to reduce the cost and/or the amount of work that it would take to survey the entire target population. A survey that measures the entire target population is called a census. A sample refers to a group or section of a population from which information is to be obtained

<span class="mw-page-title-main">Sampling (statistics)</span> Selection of data points in statistics.

In statistics, quality assurance, and survey methodology, sampling is the selection of a subset or a statistical sample of individuals from within a statistical population to estimate characteristics of the whole population. Statisticians attempt to collect samples that are representative of the population. Sampling has lower costs and faster data collection compared to recording data from the entire population, and thus, it can provide insights in cases where it is infeasible to measure an entire population.

<span class="mw-page-title-main">Focus group</span> Group interviewed to analyse opinions

A focus group is a group interview involving a small number of demographically similar people or participants who have other traits/experiences in common depending on the research objective of the study. Their reactions to specific researcher/evaluator-posed questions are studied. Focus groups are used in market research to understand better people's reactions to products or services or participants' perceptions of shared experiences. The discussions can be guided or open. In market research, focus groups can explore a group's response to a new product or service. As a program evaluation tool, they can elicit lessons learned and recommendations for performance improvement. The idea is for the researcher to understand participants' reactions. If group members are representative of a larger population, those reactions may be expected to reflect the views of that larger population. Thus, focus groups constitute a research or evaluation method that researchers organize to collect qualitative data through interactive and directed discussions.

Sampling is the use of a subset of the population to represent the whole population or to inform about (social) processes that are meaningful beyond the particular cases, individuals or sites studied. Probability sampling, or random sampling, is a sampling technique in which the probability of getting any particular sample may be calculated. In cases where external validity is not of critical importance to the study's goals or purpose, researchers might prefer to use nonprobability sampling. Nonprobability sampling does not meet this criterion. Nonprobability sampling techniques are not intended to be used to infer from the sample to the general population in statistical terms. Instead, for example, grounded theory can be produced through iterative nonprobability sampling until theoretical saturation is reached.

Survey methodology is "the study of survey methods". As a field of applied statistics concentrating on human-research surveys, survey methodology studies the sampling of individual units from a population and associated techniques of survey data collection, such as questionnaire construction and methods for improving the number and accuracy of responses to surveys. Survey methodology targets instruments or procedures that ask one or more questions that may or may not be answered.

Quantitative marketing research is the application of quantitative research techniques to the field of marketing research. It has roots in both the positivist view of the world, and the modern marketing viewpoint that marketing is an interactive process in which both the buyer and seller reach a satisfying agreement on the "four Ps" of marketing: Product, Price, Place (location) and Promotion.

<span class="mw-page-title-main">Social research</span> Research conducted by social scientists

Social research is a research conducted by social scientists following a systematic plan. Social research methodologies can be classified as quantitative and qualitative.

<span class="mw-page-title-main">Quantitative research</span> All procedures for the numerical representation of empirical facts

Quantitative research is a research strategy that focuses on quantifying the collection and analysis of data. It is formed from a deductive approach where emphasis is placed on the testing of theory, shaped by empiricist and positivist philosophies.

<span class="mw-page-title-main">Methodology</span> Study of research methods

In its most common sense, methodology is the study of research methods. However, the term can also refer to the methods themselves or to the philosophical discussion of associated background assumptions. A method is a structured procedure for bringing about a certain goal, like acquiring knowledge or verifying knowledge claims. This normally involves various steps, like choosing a sample, collecting data from this sample, and interpreting the data. The study of methods concerns a detailed description and analysis of these processes. It includes evaluative aspects by comparing different methods. This way, it is assessed what advantages and disadvantages they have and for what research goals they may be used. These descriptions and evaluations depend on philosophical background assumptions. Examples are how to conceptualize the studied phenomena and what constitutes evidence for or against them. When understood in the widest sense, methodology also includes the discussion of these more abstract issues.

<span class="mw-page-title-main">Response bias</span> Type of bias

Response bias is a general term for a wide range of tendencies for participants to respond inaccurately or falsely to questions. These biases are prevalent in research involving participant self-report, such as structured interviews or surveys. Response biases can have a large impact on the validity of questionnaires or surveys.

External validity is the validity of applying the conclusions of a scientific study outside the context of that study. In other words, it is the extent to which the results of a study can be generalized to and across other situations, people, stimuli, and times. In contrast, internal validity is the validity of conclusions drawn within the context of a particular study. Because general conclusions are almost always a goal in research, external validity is an important property of any study. Mathematical analysis of external validity concerns a determination of whether generalization across heterogeneous populations is feasible, and devising statistical and computational methods that produce valid generalizations.

In social science research, social-desirability bias is a type of response bias that is the tendency of survey respondents to answer questions in a manner that will be viewed favorably by others. It can take the form of over-reporting "good behavior" or under-reporting "bad", or undesirable behavior. The tendency poses a serious problem with conducting research with self-reports. This bias interferes with the interpretation of average tendencies as well as individual differences.

Online ethnography is an online research method that adapts ethnographic methods to the study of the communities and cultures created through computer-mediated social interaction. As modifications of the term ethnography, cyber-ethnography, online ethnography and virtual ethnography designate particular variations regarding the conduct of online fieldwork that adapts ethnographic methodology. There is no canonical approach to cyber-ethnography that prescribes how ethnography is adapted to the online setting. Instead individual researchers are left to specify their own adaptations. Netnography is another form of online ethnography or cyber-ethnography with more specific sets of guidelines and rules, and a common multidisciplinary base of literature and scholars. This article is not about a particular neologism, but the general application of ethnographic methods to online fieldwork as practiced by anthropologists, sociologists, and other scholars.

A self-report study is a type of survey, questionnaire, or poll in which respondents read the question and select a response by themselves without any outside interference. A self-report is any method which involves asking a participant about their feelings, attitudes, beliefs and so on. Examples of self-reports are questionnaires and interviews; self-reports are often used as a way of gaining participants' responses in observational studies and experiments.

Cognitive pretesting, or cognitive interviewing, is a field research method where data is collected on how the subject answers interview questions. It is the evaluation of a test or questionnaire before it's administered. It allows survey researchers to collect feedback regarding survey responses and is used in evaluating whether the question is measuring the construct the researcher intends. The data collected is then used to adjust problematic questions in the questionnaire before fielding the survey to the full sample of people.

<span class="mw-page-title-main">Unstructured interview</span> Interview in which questions are not prearranged.

An unstructured interview or non-directive interview is an interview in which questions are not prearranged. These non-directive interviews are considered to be the opposite of a structured interview which offers a set amount of standardized questions. The form of the unstructured interview varies widely, with some questions being prepared in advance in relation to a topic that the researcher or interviewer wishes to cover. They tend to be more informal and free flowing than a structured interview, much like an everyday conversation. Probing is seen to be the part of the research process that differentiates the in-depth, unstructured interview from an everyday conversation. This nature of conversation allows for spontaneity and for questions to develop during the course of the interview, which are based on the interviewees' responses. The chief feature of the unstructured interview is the idea of probe questions that are designed to be as open as possible. It is a qualitative research method and accordingly prioritizes validity and the depth of the interviewees' answers. One of the potential drawbacks is the loss of reliability, thereby making it more difficult to draw patterns among interviewees' responses in comparison to structured interviews. Unstructured interviews are used in a variety of fields and circumstances, ranging from research in social sciences, such as sociology, to college and job interviews. Fontana and Frey have identified three types of in depth, ethnographic, unstructured interviews - oral history, creative interviews, and post-modern interviews.

With the application of probability sampling in the 1930s, surveys became a standard tool for empirical research in social sciences, marketing, and official statistics. The methods involved in survey data collection are any of a number of ways in which data can be collected for a statistical survey. These are methods that are used to collect information from a sample of individuals in a systematic way. First there was the change from traditional paper-and-pencil interviewing (PAPI) to computer-assisted interviewing (CAI). Now, face-to-face surveys (CAPI), telephone surveys (CATI), and mail surveys are increasingly replaced by web surveys.

Observational methods in psychological research entail the observation and description of a subject's behavior. Researchers utilizing the observational method can exert varying amounts of control over the environment in which the observation takes place. This makes observational research a sort of middle ground between the highly controlled method of experimental design and the less structured approach of conducting interviews.

<span class="mw-page-title-main">Interview (research)</span> Research technique

An interview in qualitative research is a conversation where questions are asked to elicit information. The interviewer is usually a professional or paid researcher, sometimes trained, who poses questions to the interviewee, in an alternating series of usually brief questions and answers. They can be contrasted with focus groups in which an interviewer questions a group of people and observes the resulting conversation between interviewees, or surveys which are more anonymous and limit respondents to a range of predetermined answer choices. In addition, there are special considerations when interviewing children. In phenomenological or ethnographic research, interviews are used to uncover the meanings of central themes in the life world of the subjects from their own point of view.

References

  1. ↑ Goodman, L.A. (1961). "Snowball sampling". Annals of Mathematical Statistics. 32 (1): 148–170. doi: 10.1214/aoms/1177705148 .
  2. ↑ "Snowball Sampling". Experiment-resources.com. (accessed 8 May 2011).
  3. ↑ "Snowball sampling". changingminds.org. Retrieved 17 November 2022.
  4. 1 2 3 4 5 6 7 8 Baltar, Fabiola; Brunet, Ignasi (2012). "Social research 2.0: virtual snowball sampling method using Facebook". Internet Research. 22 (1): 55–74. doi:10.1108/10662241211199960.
  5. ↑ Heckathorn, D.D. (1997). "Respondent-Driven Sampling: A New Approach to the Study of Hidden Populations". Social Problems. 44 (2): 174–199. doi:10.1525/sp.1997.44.2.03x0221m.
  6. ↑ Salganik, M.J.; D.D. Heckathorn (2004). "Sampling and Estimation in Hidden Populations Using Respondent-Driven Sampling". Sociological Methodology. 34 (1): 193–239. doi:10.1111/j.0081-1750.2004.00152.x. S2CID   16626030.
  7. ↑ Heckathorn, D.D. (2002). "Respondent-Driven Sampling II: Deriving Valid Estimates from Chain-Referral Samples of Hidden Populations". Social Problems. 49 (1): 11–34. doi:10.1525/sp.2002.49.1.11.
  8. ↑ David L., Morgan (2008). The SAGE Encyclopedia of Qualitative Research Methods. SAGE Publications, Inc. pp. 816–817. ISBN   9781412941631.
  9. 1 2 3 4 David L., Morgan (2008). The SAGE Encyclopedia of Qualitative Research Methods. SAGE Publications, Inc. pp. 816–817. ISBN   9781412941631.
  10. ↑ Arieli, Tamar (1 June 2009). "Israeli‐Palestinian border enterprises revisited". Journal of Borderlands Studies. 24 (2): 1–14. doi:10.1080/08865655.2009.9695724. ISSN   0886-5655. S2CID   143340129.
  11. 1 2 Cohen, Nissim; Arieli, Tamar (1 July 2011). "Field research in conflict environments: Methodological challenges and snowball sampling". Journal of Peace Research. 48 (4): 423–435. doi:10.1177/0022343311405698. ISSN   0022-3433. S2CID   145328311.
  12. ↑ Marshall, Brandon DL; Kerr, Thomas; Livingstone, Chris; Li, Kathy; Montaner, Julio SG; Wood, Evan (2008). "High prevalence of HIV infection among homeless and street-involved Aboriginal youth in a Canadian setting". Harm Reduction Journal. 5 (1): 35. doi: 10.1186/1477-7517-5-35 . ISSN   1477-7517. PMC   2607257 . PMID   19019253.
  13. 1 2 Voicu, Mirela-Cristina (2011). "Using the Snowball Method in Marketing Research on Hidden Populations". Challenges of the Knowledge Society. 1: 1341–1351.
  14. ↑ "Social Research Update 33: Accessing Hidden and Hard-to-Reach Populations". sru.soc.surrey.ac.uk. Retrieved 2 April 2017.
  15. ↑ "Snowball sampling".
  16. ↑ Atkinson, Rowland; Flint, John (2004). Encyclopedia of Social Science Research Methods. SAGE Publications, Inc. pp. 1044–1045. ISBN   9780761923633.
  17. ↑ Heckathorn, Douglas D. (1997). "Respondent-Driven Sampling: A New Approach to the Study of Hidden Populations" (PDF). Social Problems. 44 (2): 174–199. doi:10.2307/3096941. JSTOR   3096941.
  18. ↑ Biernacki, Waldorf / SNOWBALL SAMPLING
  19. ↑ Brace-Govan, Jan (2004). "Issues in snowball sampling: The lawyer, the model and ethics". Qualitative Research Journal. 4 (1): 52.
  20. ↑ Browne, Kath (2005). "Snowball sampling: using social networks to research non‐heterosexual women". International Journal of Social Research Methodology. 8 (1): 47–60. doi:10.1080/1364557032000081663. S2CID   143873466.
  21. ↑ "What is Respondent Driven Sampling ?". respondentdrivensampling.org. Retrieved 17 November 2022.
  22. ↑ Dimitrios C. Christopoulos (2010). "Peer Esteem Snowballing: A methodology for expert surveys".{{cite journal}}: Cite journal requires |journal= (help)
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