For example, if you wanted to interview a sample of vegetarians cyclists people with a particular. Enhancing the sample diversity of snowball samples plos. Digest successfully predicted the presidential elections in 1920, 1924,1928, 1932 but. Because oftheconfusion surrounding thisterm, ingile and handcock 2010 we prefer, and use throughout that paper, the more precise broad category linktracing sampling while paying homage to the intellectual descent of the methods from snowball sampling. Snowball sampling can be applied for two primary purposes. They hope that the inferences they draw from their study will be maximally generalizable, statistically accurate, and useful. Heterogeneity sampling is, in this sense, almost the opposite of modal instance sampling. Freedman department of statistics university of california berkeley, ca 94720 the basic idea in sampling is extrapolation from the part to the. Advantages a it is a good representative of the population.
We may select the psus by using a specific element sampling techniques, such as simple random sampling, systematic sampling or by pps sampling. Jul 14, 2012 quota sampling ensures that the various subgroups in a population are represented on pertinent sample characteristics to the exact extent that the investigators desire it should not be confused with stratified sampling. Nonprobability sampling research methods knowledge base. Comparision of snowball sampling and sequential sampling. Snowball sampling in qualitative research sampling knowledge. This article enlists the types of sampling and sampling methods along with examples.
The use of currently enrolled research participants to recruit additional research participants sometimes referred to as the snowball sampling may be approved by the irb under some circumstances. Sampling is a procedure, where in a fraction of the data is taken from a large set of data, and the inference drawn from the sample is extended to whole group. Snowball sampling is a special nonprobability method used when there are difficulties in identifying members of the population or if the desired sample characteristic is rare. Snowball sampling is a term used for sampling procedures that allow the sampled units to provide information not only about themselves but also about other units. Snowball sampling in qualitative research sampling. Snowball sampling friend of friend you initially contact a few potential respondents and then ask them whether they know of anybody with the same characteristics that you are looking for in your research. Assessing limitations and uses of convenience samples. The question will decide the objectives on which the methodology will be based.
While these projects define themselves as global surveys, the methodology they use, and particularly the sampling methods they apply, cast doubt on the. This method is used only when the population is very hardtoreach. Rds is not a variant of either usage of snowball sampling, nor is the reverse true. Types of snowball sampling linear snowball sampling is a snowball sampling in which the researcher recruits a single participant, while the second nominee recruits the third participant. It is the sampling procedure, which will decide the accurate representation of the sample selected for the study as well as the relevance of generalization made from the research.
Snowball sampling also called network, chain referral, or reputational sampling is a method for identifying and sampling the cases in a network. We form a chain of samples and since each selection helps in the selection of next sample through the snowball effect, it is called snowball or chain sampling. One research participant refers another, and that person refers another, and that person refers anotherthus a chain of potential participants is identified. In other words, the sample starts small but snowballs into a larger sample through the. Snowball sampling isnt one of the common types of sampling methods but still valuable in certain cases. In section 6 of the present paper some results for snowball sampling based on an initial sample of the more usual kind are obtained and compared with results presented in the earlier sections of this paper obtained for snowball sampling based on an initial binomial sample. The kind of random sample will be discussed later in this section.
Raj, p4 the surveyors a person or a establishment in charge of collecting and recording data or researchers initial task is to formulate a. Then, the researcher will select each nth subject from the list. Snowball sampling also known as chainreferral sampling is a nonprobability nonrandom sampling method used when characteristics to be possessed by samples are rare and difficult to find. A manual for selecting sampling techniques in research. While in sequential sampling, sampling was taken at a given time interval and modification department of. Sampling procedure 1 of 2 sampling procedure definition sample. As implied in the first paragraph of this subsection, probability sampling must be used at each stage of the sample selection process in order for the requirements to be met. This often occurs when the population is somehow marginalized, like homeless or formerly incarcerated individuals or those who are involved in illegal activities. These actors may themselves open possibilities for an expanding web of contact. Outcome of sampling might be biased and makes difficult for all the elements of population to be part of the sample equally.
Convenience sampling involves choosing respondents at the convenience of the researcher. This sampling method generates biased samples because respondents who have great number of social connections are able to provide. Please note that some file types are incompatible with some mobile and tablet devices. According to showkat and parveen 2017, the snowball sampling method is a nonprobability sampling technique, which is also known as referral sampling, and as stated by alvi 2016, it is. In snowball sampling, you begin by identifying someone who meets the criteria for inclusion in your study. It also talks in detail about probability sampling methods and nonprobability sampling methods as well as the.
This method relies on referrals from initially sampled. Used to choose the number of participants, interviews, or work samples to use in the assessment process. Here the samples are selected based on the availability. You then ask them to recommend others who they may know who also meet the criteria. Snowball sampling is a wellknown, nonprobability method of survey sample. The snowball sampling is a research technique through survey and data registration which is. Pdf snowball sampling is a wellknown, nonprobability method of survey sample selection that is commonly used to locate hidden. Snowball sampling is an especially useful strategy when a researcher wishes to study a stigmatized group or behavior. Pdf on sep 30, 2017, mahin naderifar and others published snowball sampling. Snowball sampling is sometimes referred to as chain referral sampling. Insights from an overview of the methods literature abstract the methods literature regarding sampling in qualitative research is characterized by important inconsistencies and ambiguities, which can be problematic for students and researchers seeking a clear and coherent understanding.
For the expert interviews, a sampling strategy has been chosen that combines elements of the maximal variation and snowball sampling procedures. In this blog you will read about the types and method of snowball sampling along with its advantages and disadvantages. This technique relies on existing study participants recruiting future participants from among their acquaintances. For example, a researcher who wanted to study how people with genital herpes cope with their medical condition would be unlikely to find many participants by posting a call for interviewees in the newspaper or making an. In addition to using this sampling strategy for potentially stigmatized populations, it is also a useful strategy. Wecanuseprobabilitysamplingtechniquesonlywhenwecanhavea. Snowball sampling is a wellknown, nonprobability method of survey sample selection that is commonly used to locate hidden populations. The first purposive sampling as a tool for informant selection ma. Simple random sampling in this technique, each member of the population has an equal chance of being selected as subject.
In sociology, snowball sampling refers to a nonprobability sampling technique which includes purposive sampling in which a researcher begins with a small population of known individuals and expands the sample by asking those initial participants to identify others that should participate in the study. Snowball sampling social research update university of surrey. Sampling is defined as the process of selecting certain members or a subset of the population to make statistical inferences from them and to estimate characteristics of the whole population. Sampling bias occurs when some members of a population are systematically more likely to be selected in a sample than others. Sociology at surrey university of surrey research socialupdate. If the aim of a study is primarily explorative, qualitative and descriptive, then snowball sampling offers practical advantages hendricks, blanken and adriaans, 1992. The analysis of data from samples constitutes a major proportion of contemporary research in the social sciences. Sampling problems may differ in different parts of the population.
Snowball sampling research office oregon state university. Firstly, and most easily, as an informal method to reach a target population. In snowball sampling, the sample population is selected in a social context and in a multistage process, i. Snowball sampling is a commonly employed sampling method in qualitative research. The explanations below are meant to help you understand the reasons for using each method. History of sampling contd dates back to 1920 and started by literary digest, a news magazine published in the u. It begins with one or a few people or cases and spreads out on the basis of links to the initial cases. It also described different form of sampling method. In section 6 of the present paper some results for snowball sampling based on an initial sample of the more usual kind are obtained and compared with results presented in the earlier sections of. Using the purposive sampling method in choosing a sampling method for informant selection, the question the researcher is interested in answering is of utmost importance.
Snowball sampling problems and techniques of chain referral sampling patrick blernackl sun francisco state university dan waldorf pacific institute for research and evaluation nowball or chain referral sampling is a method that has s been widely used in qualitative sociological research. Sampling can be done through various sampling techniques in accordance with the nature of the sample as well as the subject matter of the study. Snowball sampling or chainreferral sampling is defined as a nonprobability sampling technique in which the samples have traits that are rare to find. Chapter 5 sampling 151 homelesspersonsinchicago,michaelsosin,paulcolson,andsusangrossman1988 answeredthesequestionsintheirdefinitionofthepopulationofinterest. Snowball sampling is a recruitment technique in which research participants are asked to assist researchers in identifying other potential subjects. A sampling frame is a list of the actual cases from which sample will be drawn. Researchers use this sampling method if the sample for the study is very rare or is limited to a very small subgroup of the population.
Enhancing the sample diversity of snowball samples. It is useful when the researcher know little about a group or organisation. Snowball sampling may be defined as a technique for gathering research subjects through the identification of an initial subject who is used to provide the names of other actors. In systematic random sampling, the researcher first randomly picks the first item or subject from the population. Snowball, cluster, quota, and other methods may be involved. Purposive sampling as a tool for informant selection. Randomly select individuals from that list for the sample. Disadvantages a it is a difficult and complex method of samplings. A sampling plan is a formal plan specifying a sampling method, a sample size, and procedure for recruiting participants box 1. Stratified sampling selfselection sampling cluster sampling snowball sampling probability sampling 1. The second type is exponential nondiscriminative snowball sampling where every recruited. In probability sampling, each unit is drawn with known probability, yamane, p3 or has a nonzero chance of being selected in the sample.
Pdf comparision of snowball sampling and sequential sampling. In its simplest formulation snowball sampling consists of. Common nonprobability sampling methods include convenience sampling, voluntary response sampling, purposive sampling, snowball sampling, and quota sampling. Snowball sampling is defined as a nonprobability sampling technique in which the samples have traits that are rare to find. For example, researchers use sample data from the u.
The researchers usually start with a small number of initial contacts seeds who fit the research criteria and are invited to become participants within the research. This type of sampling is also known as nonrandom sampling. The snowball strategy is a form of purposeful sampling in qualitative research that typically proceeds after a study begins and. Division of academic and student affairs office of assessment sampling procedure 1 of 2 sampling procedure definition sample. We may select all ssus for convenience or few by using a specific element sampling techniques such as simple random sampling. Using random procedures allows the use of probability sampling methods. Specifically, the paper will discuss the sampling frame suitable for case study, such as singlecase holistic and embedded, multicase, and a snowball or network sampling procedure. Discussion will also involve challenges anticipated for each procedure.
This technique relies on existing study participants recruiting. It was used in lindesmiths original study of opiate addiction 1968 as. A sampling procedure may be defined as snowball sampling when the researcher accesses informants through contact information that is provided by other informants. Snowball sampling one method that is becoming increasingly popular to recruit subjects is snowball sampling. In sociology and statistics research, snowball sampling or chain sampling, chainreferral sampling, referral sampling is a nonprobability sampling technique where existing study subjects recruit future subjects from among their acquaintances. A study on purposive sampling method in research neetij rai bikash thapa chapter i. In snowball or chain sampling, the data is collected in such a way that helps in selection of next samples too.
Failed in 1936 the literary digest poll in 1936 used a sample of 10 million, drawn from government lists of automobile and telephone. The pollster assumes that the information he is seeking can be best found from the people with age group 1630. Systematic sampling is a random sampling technique which is frequently chosen by researchers for its simplicity and its periodic quality. Snowball sampling is a special nonprobability method used when. Snowball sampling is one of the most popular methods of sampling in qualitative research, central to which are the characteristics of networking and referral. It is a methodology where researcher recruits other individuals for the study. As data collectors, you will not be responsible for selecting the sampling method. Limitations of this approach include nonrandom selection procedures.
This is a sampling technique, in which existing subjects provide referrals to recruit samples required for a research study. Snowball sampling is a nonprobability sampling technique that is used by researchers to identify potential subjects in studies where subjects are hard to locate. Recall that the sampling procedure must reflect the unit of analysis. Using social media and targeted snowball sampling to survey a. Probability sampling a term due to deming, deming is a sampling porcess that utilizes some form of random selection. A manual for selecting sampling techniques in research 4 preface the manual for sampling techniques used in social sciences is an effort to describe various types of sampling methodologies that are used in researches of social sciences in an easy and understandable way. These nonprobability sampling methods are less desirable than probability samples, but sometimes unavoidable. Raj, p10 such samples are usually selected with the help of random numbers. A qualitative sampling plan describes how many observations, interviews, focusgroup discussions or cases are needed to ensure that the findings will contribute rich data. Simple random sampling in simple random sampling, every individual in the target population has an equal chance of being part of the sample.
A purposeful method of sampling in qualitative research. For example, if you are studying the level of customer satisfaction among elite nirvana bali golf club in bali, you will find it increasingly difficult. Snowball sampling is undertaken when a qualified participant shares an invitation with other subjects similar to them who fulfill the qualifications defined for the targeted population berg, 2006. A random sample of individuals is drawn from a given finite population. Goodmans formulation requires an initial sample drawn using a probability method on a known sampling frame. The chain continues to refer linearly up to the end of the sampling. Using social media and targeted snowball sampling to. Snowball sampling a variety of procedures initial respondents are selected by probability methods. The entire process of sampling is done in a single step with each subject selected independently of the other members of the. To study the consumption pattern of households, the people living in houses, hotels, hospitals, prison etc. In purposive sampling, the items are selected in such manner that each of them are rich in information about the parameters that we are trying to study in the population in the above figure, a pollster wants to conduct a survey about the latest fashion trends in his city. An s stage k name snowball sampling procedure is defined as follows. Thus the sample group is said to grow like a rolling snowball.
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