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Comparison of Convenience Sampling and Purposive Sampling

Comparison of Convenience Sampling and Purposive Sampling American Journal of Theoretical and Applied Statistics 2016; 5(1): 1-4 Published online December 22, 2015 (http://www.sciencepublishinggroup.com/j/ajtas) doi: 10.11648/j.ajtas.20160501.11 ISSN: 2326-8999 (Print); ISSN: 2326-9006 (Online) Comparison of Convenience Sampling and Purposive Sampling Ilker Etikan, Sulaiman Abubakar Musa, Rukayya Sunusi Alkassim Department of Biostatistics, Near East University, Nicosia-TRNC, Cyprus Email address: [email protected] (I. Etikan), [email protected] (I. Etikan), [email protected] (S. A. Musa), [email protected] (R. S. Alkassim) To cite this article: Ilker Etikan, Sulaiman Abubakar Musa, Rukayya Sunusi Alkassim. Comparison of Convenience Sampling and Purposive Sampling. American Journal of Theoretical and Applied Statistics. Vol. 5, No. 1, 2016, pp. 1-4. doi: 10.11648/j.ajtas.20160501.11 Abstract: This article studied and compared the two nonprobability sampling techniques namely, Convenience Sampling and Purposive Sampling. Convenience Sampling and Purposive Sampling are Nonprobability Sampling Techniques that a researcher uses to choose a sample of subjects/units from a population. Although, Nonprobability sampling has a lot of limitations due to the subjective nature in choosing the sample and thus it is not good representative of the population, but it is useful especially when randomization is impossible like when the population is very large. It can be useful when the researcher has limited resources, time and workforce. It can also be used when the research does not aim to generate results that will be used to create generalizations pertaining to the entire population. Therefore, there is a need to use nonprobability sampling techniques. The aim of this study is to compare among the two nonrandom sampling techniques in order to know whether one technique is better or useful than the other. Different articles were reviewed to compare between Convenience Sampling and Purposive Sampling and it is concluded that the choice of the techniques (Convenience Sampling and Purposive Sampling) depends on the nature and type of the research. Keywords: Convenience Sampling, Purposive Sampling, Sampling Techniques Why would researcher consider using nonprobability 1. Introduction sampling? In some situations, the population may not be well defined. In other situations, there may not be great concern in Sample is a portion of a population or universe [20]. drawing inferences from the sample to the population. However, by population, many often consider to people only. Perhaps, the most common reason for using nonprobability Population does not necessarily mean a number of people sampling is that it is cheaper than probability sampling and [22]. It can also refer to total quantity of the things or cases can often be implemented more quickly [1]. which are the subject of our research. Probability sampling is It is very crucial for a researcher to determine which non defined as having the “distinguishing characteristic that each probability sampling technique is applicable to his study. The unit in the population has a known, nonzero chance of being technique to be used depends on the type, nature and purpose included in the sample” [8]. It is described more clearly as of the study. When subjects are chose because of the close “every participant has an equal probability of being selected” proximity to a researcher, that is, the ones that are easier for from the population [6]. In probability sampling, each the researcher to access, the researcher is making a element in the population has a known nonzero chance of convenience sampling. But for purposive sampling, a being selected through the use of a random selection researcher has something in mind and participants that suit procedure [1]. In nonprobability sampling, randomization is the purpose of the study are included. not important in selecting a sample from the population of interest. Rather, subjective methods are used to decide which elements are included in the sample. Hence, nonprobability 2. Convenience Sampling sampling is a sampling technique where the samples are In every type of research, it would be superlative to use the gathered in a process that does not give all the participants or whole population, but in most cases, it is not possible to units in the population equal chances of being included. 2 Ilker Etikan et al.: Comparison of Convenience Sampling and Purposive Sampling. include every subject because the population is almost finite. the population regarding the traits or mechanism under This is the rationale behind using sampling techniques like research. What makes convenience samples so unpredictable is convenience sampling by most researchers [5]. their vulnerability to severe hidden biases [12]. Convenience sampling (also known as Haphazard Sampling 2.1. Benchmark Problem or Accidental Sampling) is a type of nonprobability or nonrandom sampling where members of the target population A psychologist is interested in the impacts of social that meet certain practical criteria, such as easy accessibility, network on study habits of Nigerian university students. To geographical proximity, availability at a given time, or the test the whole population, the researcher would need all willingness to participate are included for the purpose of the current university students and hence, a lot of time, energy study [4]. It is also referred to the researching subjects of the and resources. population that are easily accessible to the researcher [18]. A sample would be a selection of few students from all of Convenience samples are sometimes regarded as ‘accidental the Universities in Nigeria, which the researcher has to get samples’ because elements may be selected in the sample for the testing. simply as they just happen to be situated, spatially or The convenience sample here would be a group of students administratively, near to where the researcher is conducting the from Abubakar Tafawa Balewa University, Bauchi, a Nigerian data collection. Ecological data are often taken using University where the Psychologist is working as lecturer. convenience sampling, here data are collected along roads, We learnt from the above that, the psychologist was trails or utility corridors and hence are not representative of subjective as the only students of Abubakar Tafawa Balewa population of interest. Other example of convenience sampling University, Bauchi were included in the study. With this include data taken subjectively near camp, around parking sample the researcher would utilize little time and resource. areas, or an areas where density is known to be high. Biologist The selected students in this study are different from other often use convenience sampling in the field work because it is Nigerian University students. Thus, this may undermine the easier like walking on a road and stop occasionally to record ability of the Psychologist to make generalisations from the numbers. With numbers derive from convenience sampling, sample to the population. one can make only weak statement about some characteristic Therefore, in convenience sampling, the individuals of the sample itself rather than a formal inductive inference selected by the researcher may not be applicable to the concerning the population of interest. Further explains that, research problem. Hence, there is a risk of collecting poor “captive participants such as students in the researcher’s own quality data due to poor research outcomes and as such, institution are main examples of convenience sampling” [4]. difficult to convince others to accept the findings of research Convenience Sampling is affordable, easy and the subjects based on poor foundation [16]. Some methods literature are readily available. It is compulsory for the researcher to disregards convenience sampling as being an inappropriate describe how the sample would differ from the one that was method in social research due to the severe limitations [12]. randomly selected. It is also necessary to describe the subjects who might be excluded during the selection process or the 2.2. Purposive Sampling subjects who are overrepresented in the sample [5]. The main Data gathering is crucial in research, as the data is meant to objective of convenience sampling is to collect information contribute to a better understanding of a theoretical framework from participants who are easily accessible to the researcher [2]. It then becomes imperious that selecting the manner of like recruiting providers attending a staff meeting for study obtaining data and from whom the data will be acquired be participation. Although commonly used, it is neither done with sound judgment, especially since no amount of purposeful nor strategic [11]. The main assumption associated analysis can make up for improperly collected data [21]. The with convenience sampling is that the members of the target purposive sampling technique, also called judgment sampling, population are homogeneous. That is, that there would be no is the deliberate choice of a participant due to the qualities the difference in the research results obtained from a random participant possesses. It is a nonrandom technique that does sample, a nearby sample, a co-operative sample, or a sample not need underlying theories or a set number of participants. gathered in some inaccessible part of the population [10]. Simply put, the researcher decides what needs to be known Point out that the obvious disadvantage of convenience and sets out to find people who can and are willing to provide sampling is that it is likely to be biased [13]. They advise the information by virtue of knowledge or experience [2]. It is researchers that the convenience sampling should not be taken typically used in qualitative research to identify and select the to be representative of the population. Still, there is another information-rich cases for the most proper utilization of problem of great concern related to convenience sampling, i.e. available resources [17]. This involves identification and the problem of outliers. Because of the high self-selection selection of individuals or groups of individuals that are possibility in non-probability sampling, the effect of outliers proficient and well-informed with a phenomenon of interest can be more devastating in this kind of subject selection. [3]. In addition to knowledge and experience, [2] and [19] note Outliers are cases whom consider as not belonging to the data. the importance of availability and willingness to participate, In a convenience sample, on the contrary, neither biases nor and the ability to communicate experiences and opinions in an their probabilities are quantified [7]. In fact, the researcher articulate, expressive, and reflective manner. Unlike random does not know how well a convenience sample will represent American Journal of Theoretical and Applied Statistics 2016; 5(1): 1-4 3 studies, which deliberately include a diverse cross section of or where funds are limited, Critical Case Sampling is a ages, backgrounds and cultures, the idea behind purposive method where a select number of important or “critical” sampling is to concentrate on people with particular cases are selected and then examined. The criterion for characteristics who will better be able to assist with the deciding whether or not an example is “critical” is generally relevant research. decided using the following statements: “If it happens there, will it happen anywhere?” or “if that group is having problems, then can we be sure all the groups are having 3. Purposive Sampling Methods problems?” 3.1. Maximum Variation Sampling 3.6. Total Population Sampling The idea behind MVS is to look at a subject from all available On occasion, it may be that leaving out certain cases from angles, thereby achieving a greater understanding. Also known your sampling would be as if you had an incomplete puzzle - as "Heterogeneous Sampling", it involves selecting candidates with obvious pieces missing. In this instance, the best across a broad spectrum relating to the topic of study. For sampling method to use is Total Population Sampling. TPS is example, if one was researching an education program would a technique where the entire population that meet the criteria include students who hated the program, students classed as (e.g. specific skill set, experience, etc.) are included in the “typical” and students who excelled. This type of sampling is research being conducted. Total Population Sampling is more useful when a random sample is not taken, for instance, if the commonly used where the number of cases being sample pool is too small. investigated is relatively small. 3.2. Homogeneous Sampling 3.7. Expert Sampling This form of sampling, unlike MVS, focuses on candidates As indicated by the name, Expert Sampling calls for who share similar traits or specific characteristics. For experts in a particular field to be the subjects of the purposive example, participants in Homogenous Sampling would be sampling. This sort of sampling is useful when the research is similar in terms of ages, cultures, jobs or life experiences. expected to take a long time before it provides conclusive The idea is to focus on this precise similarity and how it results or where there is currently a lack of observational relates to the topic being researched. For example, if one was evidence. Expert sampling is a positive tool to use when researching long-term side effects of working with asbestos, investigating new areas of research, to garner whether or not for a Homogenous Sampling, the only people who had further study would be worth the effort. worked with asbestos for 20 years or longer are included. 3.3. Typical Case Sampling 4. Benchmark Problem TCS is useful when a researcher is dealing with large A data analyst wants to get an opinion from pregnant programs, it helps set the bar of what is standard or “typical”. nd women who attend second Ante Natal Care (ANC2 or 2 Candidates are generally chosen based on their likelihood of ANC) pertaining their pregnancy in Kano State of Nigeria for behaving like everyone else. For example, if one was the month of October, 2015. The analyst goes to the health th researching the reactions of 9 grade students to a job facilities offering Ante Natal Care service and then focus on placement program, would select classes from similar socio- pregnant women that come for Second ANC (ANC2). economic regions, as opposed to selecting a class from an a Here, the analyst’s target is pregnant women who come for poorer inner city school, another from a mid-west farming second ANC and those who come for first, third and 4 or community, and another from an affluent private school. more ANCs are excluded. That is the purposive sampling because it starts with a purpose in mind and the sample is 3.4. Extreme/Deviant Case Sampling thus selected to include people of interest and exclude those The polar opposite of Typical Case Sampling, Extreme (or who do not suit the purpose. Deviant) Case Sampling is designed to focus on individuals that are unusual or atypical. This form of sampling is more 5. Convenience Sampling Versus often used when researchers are developing “best in practice” guidelines or are looking into “what not to do”. An example Purposive Sampling would be a study into heart surgery patients who recovered Convenience sampling technique is applicable to both significantly faster or slower than average. Researchers qualitative and quantitative studies, although it is most would be looking for variations in these cases to explain why frequently used in quantitative studies while purposive their recoveries were atypical. sampling is typically used in qualitative studies [5]. 3.5. Critical Case Sampling Quantitative methods are intended to achieve breadth of understanding while qualitative methods are for the most part, Extremely popular in the initial stages of research to intended to achieve depth of understanding [17]. Observe, determine whether or not a more in depth study is warranted, whether the technique employed is convenience sampling or 4 Ilker Etikan et al.: Comparison of Convenience Sampling and Purposive Sampling. [4] Dörnyei, Z. (2007). Research methods in applied linguistics. purposive sampling, validity and efficiency are of utmost New York: Oxford University Press. important [15]. However, sampling must be consistent with the assumptions and objectives essential in the use of either [5] Explorable.com. (2009, Sep 16). Convenience Sampling. convenience sampling or purposive sampling. Purposive Retrieved Nov 13, 2015, from https://explorable.com/convenience-sampling sampling methods place primary emphasis on saturation (i.e., obtaining a comprehensive understanding by continuing to [6] Fink, Arlene. How to Sample in Surveys. Vol. 6. London: sample until no new substantive information is acquired) [14]. Sage Publications, 1995. Convenience sampling methods place primary emphasis on [7] Hatch, E. & Lazaraton, A. (1991). The research manual: generalizability (i.e., ensuring that the knowledge gained is Design and statistics for applied linguistics. New York: representative of the population from which the sample was Newbury House Publishers. drawn). Each methodology, in turn, has different expectations [8] Henry, Gary T. Practical Sampling. Vol. 21. London: Sage and standards for determining the number of participants Publications, 1990. required to achieve its aims. In convenience sampling, researcher selects subjects that are more readily accessible, [9] http://dissertation.laerd.com/purposive-sampling.php#types. Thus, opportunity to participate is not equal for all qualified [10] http://www.unesco.org/iiep. individuals in the target population and study results are not necessarily generalizable to the population, while in [11] Lawrence A Palinkas, Carla A Green, Jennifer P Wisdom, & purposive Sampling, subjects are selected based on study Kimberly Eaton Hoagwood. (2013). Purposeful Sampling for Qualitative Data Collection and Analysis in Mixed Method purpose with the expectation that each participant will Implementation Research. Reearch Gate. provide unique and rich information of value to the study. As sample size increase the statistical power of the convenience [12] Leiner, D. J. (2014). Convenience Samples and Respondent sample also increases while in purposive sampling, Sample Pools. 1-36. size is determined by data saturation not by statistical power [13] Mackey, A. & Gass, S. (2005). Second language research: analysis [23]. Methodology and design. New Jersey: Lawrence Erlbaum Associates, Inc. 6. Conclusion [14] Miles, M. B., & Huberman, A. M. (1994). Qualitative data analysis: An expanded sourcebook (2nd ed.). Thousand Oaks, The above comparison shows that, both convenience CA: Sage. sampling and purposive sampling share some limitations [15] Morse, J. M., & Niehaus, L. (2009). Mixed method design: which include nonrandom selection of participants, that is to Principles and procedures. Walnut Creek, CA: Left Coast say the researcher is subjective and bias in choosing the Press. subjects of the study. This impedes the researcher’s ability to draw inferences about a population. The study also shows [16] Oppong, S. H. (2013). The problem of sampling in qualitative research. Asian journal of management sciences and that although, convenience sampling can be used in both education, 1-9. qualitative and quantitative study, but it is frequently used in quantitative study while purposive sampling is typically used [17] Patton, M. Q. (2002). Qualitative research and evaluation in qualitative study. Purposive sampling technique cannot be methods 3rd ed. Thousand Oaks, CA: Sage. used when the variables in the study are quantitative in nature [18] S. K., & Given Lisa M. (2008). Convenience Sample. In The and also in convenience sampling, the nature of the research SAGE Encyclopedia of Qualitative Research Methods. is mostly quantitative. Thus, the choice of technique to be Thousand Oaks, CA: Sage. used depends on the type and nature of the study. [19] Spradley, J. P. (1979). The ethnographic interview. New York: Holt, Rinehart & Winston. [20] Tailor, G. R. (Ed.). (2005). Integrating quantitative and References qualitative methods in research. Maryland: University Press of [1] Battaglia, M. P. (2008). Non Probability Sampling . America Inc. Encyclopedia of Survey Resesrch Methods. 2008. SAGE [21] Tongco, M. D. (nd). Purposive Sampling as a Tool for Publications, 1-4. Informant Selection. A Journal of Plant, People and Applied [2] Bernard, H. R. (2002). Research methods in anthropology: Research Ethnobotany Research and Applications, 1-12. Qualitative and quantitative approaches (3rd ed.). Walnut [22] Walliman, N. (2011). Research methods: The basics. New Creek, CA: Alta Mira Press. York: Rout ledge. [3] Cresswell, J. W., & Plano Clark, V. L. (2011). Designing and [23] Zhi., H. L. (2014). A comparison of convenience sampling and Conducting mixed method research (2nd ed.). Thousand Oaks, purposive sampling. PubMed, 105-11. CA: Sage. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Theoretical and Applied Statistics Unpaywall

Comparison of Convenience Sampling and Purposive Sampling

American Journal of Theoretical and Applied StatisticsJan 1, 2016

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American Journal of Theoretical and Applied Statistics 2016; 5(1): 1-4 Published online December 22, 2015 (http://www.sciencepublishinggroup.com/j/ajtas) doi: 10.11648/j.ajtas.20160501.11 ISSN: 2326-8999 (Print); ISSN: 2326-9006 (Online) Comparison of Convenience Sampling and Purposive Sampling Ilker Etikan, Sulaiman Abubakar Musa, Rukayya Sunusi Alkassim Department of Biostatistics, Near East University, Nicosia-TRNC, Cyprus Email address: [email protected] (I. Etikan), [email protected] (I. Etikan), [email protected] (S. A. Musa), [email protected] (R. S. Alkassim) To cite this article: Ilker Etikan, Sulaiman Abubakar Musa, Rukayya Sunusi Alkassim. Comparison of Convenience Sampling and Purposive Sampling. American Journal of Theoretical and Applied Statistics. Vol. 5, No. 1, 2016, pp. 1-4. doi: 10.11648/j.ajtas.20160501.11 Abstract: This article studied and compared the two nonprobability sampling techniques namely, Convenience Sampling and Purposive Sampling. Convenience Sampling and Purposive Sampling are Nonprobability Sampling Techniques that a researcher uses to choose a sample of subjects/units from a population. Although, Nonprobability sampling has a lot of limitations due to the subjective nature in choosing the sample and thus it is not good representative of the population, but it is useful especially when randomization is impossible like when the population is very large. It can be useful when the researcher has limited resources, time and workforce. It can also be used when the research does not aim to generate results that will be used to create generalizations pertaining to the entire population. Therefore, there is a need to use nonprobability sampling techniques. The aim of this study is to compare among the two nonrandom sampling techniques in order to know whether one technique is better or useful than the other. Different articles were reviewed to compare between Convenience Sampling and Purposive Sampling and it is concluded that the choice of the techniques (Convenience Sampling and Purposive Sampling) depends on the nature and type of the research. Keywords: Convenience Sampling, Purposive Sampling, Sampling Techniques Why would researcher consider using nonprobability 1. Introduction sampling? In some situations, the population may not be well defined. In other situations, there may not be great concern in Sample is a portion of a population or universe [20]. drawing inferences from the sample to the population. However, by population, many often consider to people only. Perhaps, the most common reason for using nonprobability Population does not necessarily mean a number of people sampling is that it is cheaper than probability sampling and [22]. It can also refer to total quantity of the things or cases can often be implemented more quickly [1]. which are the subject of our research. Probability sampling is It is very crucial for a researcher to determine which non defined as having the “distinguishing characteristic that each probability sampling technique is applicable to his study. The unit in the population has a known, nonzero chance of being technique to be used depends on the type, nature and purpose included in the sample” [8]. It is described more clearly as of the study. When subjects are chose because of the close “every participant has an equal probability of being selected” proximity to a researcher, that is, the ones that are easier for from the population [6]. In probability sampling, each the researcher to access, the researcher is making a element in the population has a known nonzero chance of convenience sampling. But for purposive sampling, a being selected through the use of a random selection researcher has something in mind and participants that suit procedure [1]. In nonprobability sampling, randomization is the purpose of the study are included. not important in selecting a sample from the population of interest. Rather, subjective methods are used to decide which elements are included in the sample. Hence, nonprobability 2. Convenience Sampling sampling is a sampling technique where the samples are In every type of research, it would be superlative to use the gathered in a process that does not give all the participants or whole population, but in most cases, it is not possible to units in the population equal chances of being included. 2 Ilker Etikan et al.: Comparison of Convenience Sampling and Purposive Sampling. include every subject because the population is almost finite. the population regarding the traits or mechanism under This is the rationale behind using sampling techniques like research. What makes convenience samples so unpredictable is convenience sampling by most researchers [5]. their vulnerability to severe hidden biases [12]. Convenience sampling (also known as Haphazard Sampling 2.1. Benchmark Problem or Accidental Sampling) is a type of nonprobability or nonrandom sampling where members of the target population A psychologist is interested in the impacts of social that meet certain practical criteria, such as easy accessibility, network on study habits of Nigerian university students. To geographical proximity, availability at a given time, or the test the whole population, the researcher would need all willingness to participate are included for the purpose of the current university students and hence, a lot of time, energy study [4]. It is also referred to the researching subjects of the and resources. population that are easily accessible to the researcher [18]. A sample would be a selection of few students from all of Convenience samples are sometimes regarded as ‘accidental the Universities in Nigeria, which the researcher has to get samples’ because elements may be selected in the sample for the testing. simply as they just happen to be situated, spatially or The convenience sample here would be a group of students administratively, near to where the researcher is conducting the from Abubakar Tafawa Balewa University, Bauchi, a Nigerian data collection. Ecological data are often taken using University where the Psychologist is working as lecturer. convenience sampling, here data are collected along roads, We learnt from the above that, the psychologist was trails or utility corridors and hence are not representative of subjective as the only students of Abubakar Tafawa Balewa population of interest. Other example of convenience sampling University, Bauchi were included in the study. With this include data taken subjectively near camp, around parking sample the researcher would utilize little time and resource. areas, or an areas where density is known to be high. Biologist The selected students in this study are different from other often use convenience sampling in the field work because it is Nigerian University students. Thus, this may undermine the easier like walking on a road and stop occasionally to record ability of the Psychologist to make generalisations from the numbers. With numbers derive from convenience sampling, sample to the population. one can make only weak statement about some characteristic Therefore, in convenience sampling, the individuals of the sample itself rather than a formal inductive inference selected by the researcher may not be applicable to the concerning the population of interest. Further explains that, research problem. Hence, there is a risk of collecting poor “captive participants such as students in the researcher’s own quality data due to poor research outcomes and as such, institution are main examples of convenience sampling” [4]. difficult to convince others to accept the findings of research Convenience Sampling is affordable, easy and the subjects based on poor foundation [16]. Some methods literature are readily available. It is compulsory for the researcher to disregards convenience sampling as being an inappropriate describe how the sample would differ from the one that was method in social research due to the severe limitations [12]. randomly selected. It is also necessary to describe the subjects who might be excluded during the selection process or the 2.2. Purposive Sampling subjects who are overrepresented in the sample [5]. The main Data gathering is crucial in research, as the data is meant to objective of convenience sampling is to collect information contribute to a better understanding of a theoretical framework from participants who are easily accessible to the researcher [2]. It then becomes imperious that selecting the manner of like recruiting providers attending a staff meeting for study obtaining data and from whom the data will be acquired be participation. Although commonly used, it is neither done with sound judgment, especially since no amount of purposeful nor strategic [11]. The main assumption associated analysis can make up for improperly collected data [21]. The with convenience sampling is that the members of the target purposive sampling technique, also called judgment sampling, population are homogeneous. That is, that there would be no is the deliberate choice of a participant due to the qualities the difference in the research results obtained from a random participant possesses. It is a nonrandom technique that does sample, a nearby sample, a co-operative sample, or a sample not need underlying theories or a set number of participants. gathered in some inaccessible part of the population [10]. Simply put, the researcher decides what needs to be known Point out that the obvious disadvantage of convenience and sets out to find people who can and are willing to provide sampling is that it is likely to be biased [13]. They advise the information by virtue of knowledge or experience [2]. It is researchers that the convenience sampling should not be taken typically used in qualitative research to identify and select the to be representative of the population. Still, there is another information-rich cases for the most proper utilization of problem of great concern related to convenience sampling, i.e. available resources [17]. This involves identification and the problem of outliers. Because of the high self-selection selection of individuals or groups of individuals that are possibility in non-probability sampling, the effect of outliers proficient and well-informed with a phenomenon of interest can be more devastating in this kind of subject selection. [3]. In addition to knowledge and experience, [2] and [19] note Outliers are cases whom consider as not belonging to the data. the importance of availability and willingness to participate, In a convenience sample, on the contrary, neither biases nor and the ability to communicate experiences and opinions in an their probabilities are quantified [7]. In fact, the researcher articulate, expressive, and reflective manner. Unlike random does not know how well a convenience sample will represent American Journal of Theoretical and Applied Statistics 2016; 5(1): 1-4 3 studies, which deliberately include a diverse cross section of or where funds are limited, Critical Case Sampling is a ages, backgrounds and cultures, the idea behind purposive method where a select number of important or “critical” sampling is to concentrate on people with particular cases are selected and then examined. The criterion for characteristics who will better be able to assist with the deciding whether or not an example is “critical” is generally relevant research. decided using the following statements: “If it happens there, will it happen anywhere?” or “if that group is having problems, then can we be sure all the groups are having 3. Purposive Sampling Methods problems?” 3.1. Maximum Variation Sampling 3.6. Total Population Sampling The idea behind MVS is to look at a subject from all available On occasion, it may be that leaving out certain cases from angles, thereby achieving a greater understanding. Also known your sampling would be as if you had an incomplete puzzle - as "Heterogeneous Sampling", it involves selecting candidates with obvious pieces missing. In this instance, the best across a broad spectrum relating to the topic of study. For sampling method to use is Total Population Sampling. TPS is example, if one was researching an education program would a technique where the entire population that meet the criteria include students who hated the program, students classed as (e.g. specific skill set, experience, etc.) are included in the “typical” and students who excelled. This type of sampling is research being conducted. Total Population Sampling is more useful when a random sample is not taken, for instance, if the commonly used where the number of cases being sample pool is too small. investigated is relatively small. 3.2. Homogeneous Sampling 3.7. Expert Sampling This form of sampling, unlike MVS, focuses on candidates As indicated by the name, Expert Sampling calls for who share similar traits or specific characteristics. For experts in a particular field to be the subjects of the purposive example, participants in Homogenous Sampling would be sampling. This sort of sampling is useful when the research is similar in terms of ages, cultures, jobs or life experiences. expected to take a long time before it provides conclusive The idea is to focus on this precise similarity and how it results or where there is currently a lack of observational relates to the topic being researched. For example, if one was evidence. Expert sampling is a positive tool to use when researching long-term side effects of working with asbestos, investigating new areas of research, to garner whether or not for a Homogenous Sampling, the only people who had further study would be worth the effort. worked with asbestos for 20 years or longer are included. 3.3. Typical Case Sampling 4. Benchmark Problem TCS is useful when a researcher is dealing with large A data analyst wants to get an opinion from pregnant programs, it helps set the bar of what is standard or “typical”. nd women who attend second Ante Natal Care (ANC2 or 2 Candidates are generally chosen based on their likelihood of ANC) pertaining their pregnancy in Kano State of Nigeria for behaving like everyone else. For example, if one was the month of October, 2015. The analyst goes to the health th researching the reactions of 9 grade students to a job facilities offering Ante Natal Care service and then focus on placement program, would select classes from similar socio- pregnant women that come for Second ANC (ANC2). economic regions, as opposed to selecting a class from an a Here, the analyst’s target is pregnant women who come for poorer inner city school, another from a mid-west farming second ANC and those who come for first, third and 4 or community, and another from an affluent private school. more ANCs are excluded. That is the purposive sampling because it starts with a purpose in mind and the sample is 3.4. Extreme/Deviant Case Sampling thus selected to include people of interest and exclude those The polar opposite of Typical Case Sampling, Extreme (or who do not suit the purpose. Deviant) Case Sampling is designed to focus on individuals that are unusual or atypical. This form of sampling is more 5. Convenience Sampling Versus often used when researchers are developing “best in practice” guidelines or are looking into “what not to do”. An example Purposive Sampling would be a study into heart surgery patients who recovered Convenience sampling technique is applicable to both significantly faster or slower than average. Researchers qualitative and quantitative studies, although it is most would be looking for variations in these cases to explain why frequently used in quantitative studies while purposive their recoveries were atypical. sampling is typically used in qualitative studies [5]. 3.5. Critical Case Sampling Quantitative methods are intended to achieve breadth of understanding while qualitative methods are for the most part, Extremely popular in the initial stages of research to intended to achieve depth of understanding [17]. Observe, determine whether or not a more in depth study is warranted, whether the technique employed is convenience sampling or 4 Ilker Etikan et al.: Comparison of Convenience Sampling and Purposive Sampling. [4] Dörnyei, Z. (2007). Research methods in applied linguistics. purposive sampling, validity and efficiency are of utmost New York: Oxford University Press. important [15]. However, sampling must be consistent with the assumptions and objectives essential in the use of either [5] Explorable.com. (2009, Sep 16). Convenience Sampling. convenience sampling or purposive sampling. Purposive Retrieved Nov 13, 2015, from https://explorable.com/convenience-sampling sampling methods place primary emphasis on saturation (i.e., obtaining a comprehensive understanding by continuing to [6] Fink, Arlene. How to Sample in Surveys. Vol. 6. London: sample until no new substantive information is acquired) [14]. Sage Publications, 1995. Convenience sampling methods place primary emphasis on [7] Hatch, E. & Lazaraton, A. (1991). The research manual: generalizability (i.e., ensuring that the knowledge gained is Design and statistics for applied linguistics. New York: representative of the population from which the sample was Newbury House Publishers. drawn). Each methodology, in turn, has different expectations [8] Henry, Gary T. Practical Sampling. Vol. 21. London: Sage and standards for determining the number of participants Publications, 1990. required to achieve its aims. In convenience sampling, researcher selects subjects that are more readily accessible, [9] http://dissertation.laerd.com/purposive-sampling.php#types. Thus, opportunity to participate is not equal for all qualified [10] http://www.unesco.org/iiep. individuals in the target population and study results are not necessarily generalizable to the population, while in [11] Lawrence A Palinkas, Carla A Green, Jennifer P Wisdom, & purposive Sampling, subjects are selected based on study Kimberly Eaton Hoagwood. (2013). Purposeful Sampling for Qualitative Data Collection and Analysis in Mixed Method purpose with the expectation that each participant will Implementation Research. Reearch Gate. provide unique and rich information of value to the study. As sample size increase the statistical power of the convenience [12] Leiner, D. J. (2014). Convenience Samples and Respondent sample also increases while in purposive sampling, Sample Pools. 1-36. size is determined by data saturation not by statistical power [13] Mackey, A. & Gass, S. (2005). Second language research: analysis [23]. Methodology and design. New Jersey: Lawrence Erlbaum Associates, Inc. 6. Conclusion [14] Miles, M. B., & Huberman, A. M. (1994). Qualitative data analysis: An expanded sourcebook (2nd ed.). Thousand Oaks, The above comparison shows that, both convenience CA: Sage. sampling and purposive sampling share some limitations [15] Morse, J. M., & Niehaus, L. (2009). Mixed method design: which include nonrandom selection of participants, that is to Principles and procedures. Walnut Creek, CA: Left Coast say the researcher is subjective and bias in choosing the Press. subjects of the study. This impedes the researcher’s ability to draw inferences about a population. The study also shows [16] Oppong, S. H. (2013). The problem of sampling in qualitative research. Asian journal of management sciences and that although, convenience sampling can be used in both education, 1-9. qualitative and quantitative study, but it is frequently used in quantitative study while purposive sampling is typically used [17] Patton, M. Q. (2002). Qualitative research and evaluation in qualitative study. Purposive sampling technique cannot be methods 3rd ed. Thousand Oaks, CA: Sage. used when the variables in the study are quantitative in nature [18] S. K., & Given Lisa M. (2008). Convenience Sample. In The and also in convenience sampling, the nature of the research SAGE Encyclopedia of Qualitative Research Methods. is mostly quantitative. Thus, the choice of technique to be Thousand Oaks, CA: Sage. used depends on the type and nature of the study. [19] Spradley, J. P. (1979). The ethnographic interview. New York: Holt, Rinehart & Winston. [20] Tailor, G. R. (Ed.). (2005). Integrating quantitative and References qualitative methods in research. Maryland: University Press of [1] Battaglia, M. P. (2008). Non Probability Sampling . America Inc. Encyclopedia of Survey Resesrch Methods. 2008. SAGE [21] Tongco, M. D. (nd). Purposive Sampling as a Tool for Publications, 1-4. Informant Selection. A Journal of Plant, People and Applied [2] Bernard, H. R. (2002). Research methods in anthropology: Research Ethnobotany Research and Applications, 1-12. Qualitative and quantitative approaches (3rd ed.). Walnut [22] Walliman, N. (2011). Research methods: The basics. New Creek, CA: Alta Mira Press. York: Rout ledge. [3] Cresswell, J. W., & Plano Clark, V. L. (2011). Designing and [23] Zhi., H. L. (2014). A comparison of convenience sampling and Conducting mixed method research (2nd ed.). Thousand Oaks, purposive sampling. PubMed, 105-11. CA: Sage.

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American Journal of Theoretical and Applied StatisticsUnpaywall

Published: Jan 1, 2016

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