Biometrics & Biostatistics International Journal Comparision of Snowball Sampling and Sequential Sampling Technique Submit Manuscript | http://medcraveonline.com Introduction Representing against population with a subset of it is termed as sampling. Sampling can either be statistical or non-statistical. In statistical sampling (probability sampling technique) calculating the probability of getting any particular sample is possible. It is scientific and every element stands an equal chance of being selected. In statistical sampling, workforce, time and money highly limits most researchers from getting true random sample that will represent the entire population. Thus, a non- probability sampling techniques are needed. Non-probability sampling techniques help researchers to subjectively select unit that represents the population under study. Unlike probability sampling, non-probability sampling does not involve random selection rather samples are selected based on accessibility. In applied social researches, non probabilistic methods are used especially when random sampling is not theoretically, practically and feasibly sensible. This paper will review two exemplary non- probability sampling techniques, namely; snowball sampling and sequential sampling met Snowball Sampling Snowball sampling or Chain-referral-sampling of a hidden population begins with a convenience sample of initial subject, because if a random sample could be drawn, the population would not restrict as hidden. This initial subject serve as “seeds,” through which wave 1 subject is recruited; wave 1 subject in turn recruit wave 2 subjects; and the sample consequently expands wave by wave like a snowball growing in size as it rolls down a hill [1]. This sampling method generates biased samples because respondents who have great number of social connections are able to provide investigators with a higher proportion of other respondents who have characteristics similar to that initial respondent [2]. The impossibility of making unbiased estimate from snowball samples was believed, but snowball sampling variation is called respondent-driven sampling. It allows the researcher to make asymptotically unbiased estimates from snowball samples under some conditions [3]. Hence Snowball sampling and respondent-driven sampling allow participants to make estimates about the social network connecting the hidden population. One of the most well-known forms of non-probability sampling is the snowball sampling method, which is particularly suitable when the population of interest is hard to reach and compiling a list of the population poses difficulties for the researcher. Common examples of the use of snowball sampling involve sociological studies into hidden populations that may be involved in sensitive issues or illegal activities, such as drug use and prostitution [4]. As with random sampling, the snowballing method is not as uncontrolled as its name implied. The researcher is deeply involved in developing and managing the origination and progress of the sample, and seeks to ensure at all times that the chain of referrals remains within limitations that are relevant to the study. One of the dangers with snowball sampling is that respondents often suggest others who share similar characteristics, or the same outlook, and it is also compulsory on the researcher to ensure that the initial set of respondents is sufficiently varied so that the sample is not skewed excessively in any one particular direction. 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. The chain continues to refer linearly up to the end of the sampling. The second type is Exponential Non-Discriminative Snowball Sampling where every recruited participant in the research work recruits another participant while in the exponential discriminative snowball sampling not every recruited participant is going to recruit another participant; the chain is discriminating [5]. One of the most important uses of Volume 3 Issue 1 - 2015 Department of Biostatistics, Near East University, Nicosia- TRNC, Cyprus *Corresponding author: Ilker Etikan, Near East University, Nicosia-TRNC, Cyprus, Email: Received: November 18, 2015 | Published: December 09, 2015 Review Article Biom Biostat Int J 2015, 3(1): 00055 Abstract The article provides the description and comparison of two non-random samplings which are snowball or chain referral sampling and sequential sampling. Snowball sampling has been widely used in qualitative sociological research, especially in the study of deviant behavior and is used in the place where the population is hard to reach. It also described different form of sampling method. While in sequential sampling, sampling was taken at a given time interval and modification can be made by correcting the research and sampling method to centralize the analysis and make a satisfied decision.