Student Resources How and Why Sampling Is Used in Psychology Research By Kendra Cherry, MSEd Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book." Learn about our editorial process Updated on November 18, 2023 Fact checked Verywell Mind content is rigorously reviewed by a team of qualified and experienced fact checkers. Fact checkers review articles for factual accuracy, relevance, and timeliness. We rely on the most current and reputable sources, which are cited in the text and listed at the bottom of each article. Content is fact checked after it has been edited and before publication. Learn more. by Emily Swaim Fact checked by Emily Swaim Emily Swaim is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, and Vox. Learn about our editorial process Print Verywell / Nusha Ashjaee Table of Contents View All Table of Contents Why Use Samples Probability Samples Nonprobability Samples Sampling Errors Close In statistics, a sample is a subset of a population that is used to represent the entire group as a whole. When doing psychology research, it is often impractical to survey every member of a particular population because the number of people is simply too large. To make inferences about the characteristics of a population, psychology researchers use a random sample. Keep reading to learn about how samples are used in psychology research, the different types of samples, and the errors that may occur when using samples. Why Psychology Researchers Use Samples When researching an aspect of the human mind or human behavior, psychology researchers can rarely collect data from every single affected individual. Instead, they use a smaller sample of individuals to represent the larger group. The goal when choosing a sample is to make sure it represents the entire group accurately. This means that the sample should reflect the diverse characteristics present in the total population. The sample must accurately represent the population in question so researchers can generalize their results to the larger group with statistical analysis. In psychological research and other types of social science research, experimenters typically rely on a few different sampling methods. These can be grouped into probability and nonprobability samples. Types of Probability Samples Probability sampling means every individual in a population stands a chance of being selected. Because probability sampling uses random selection, every subset of the population has an equal chance of being represented in the sample. Probability samples are more representative of large populations and researchers are better able to generalize their results to the group as a whole when they use probability samples. Simple Random Sampling Simple random sampling is, as the name suggests, the simplest type of probability sampling. Psychology researchers take every individual in a population and randomly select individuals to compose their sample, often by using some type of computer program or random number generator. Stratified Random Sampling Stratified random sampling involves separating the population into subgroups and then taking a simple random sample from each of these subgroups. For example, researchers may divide the population into subgroups based on race, sex, or age, and then take a simple random sample of each of these groups. Stratified random sampling often provides greater statistical accuracy than simple random sampling because it ensures each of the subgroups is accurately represented in the sample. Cluster Sampling Cluster sampling involves dividing a population into smaller clusters, often based on geographic location. A random sample of these clusters is then selected, and all of the subjects within the cluster are measured. For example, imagine you are doing a study on school principals in your state. Collecting data from every single school principal would be cost-prohibitive and time-consuming. But, if you were to use a cluster sampling method, you would randomly select five counties from your state and then collect data from every subject in each of those five counties to create a representative sample. Recap Probability sampling methods allow psychology researchers to get a more representative sample. Techniques that might be used include simple random sampling, stratified random sampling, and cluster sampling. Introduction to Research Methods in Psychology Types of Nonprobability Samples Nonprobability sampling involves selecting participants using methods that do not give every subset of a population an equal chance of being represented. For example, a study may recruit participants from an already established group of volunteers. One problem with this type of sample is that volunteers might differ from non-volunteers on certain variables, which can make it difficult to generalize the results to the entire population. Convenience Sampling Convenience sampling involves selecting participants for a study based on what is most convenient–people who are easily accessible and have the time. If you have ever volunteered for a psychology study conducted through your university's psychology department, then you have participated in a study that relied on a convenience sample. Studies that rely on asking for volunteers or using clinical samples available to the researcher are also examples of convenience samples. How Snowball Sampling Used in Psychology Research Purposive Sampling Purposive sampling involves seeking out individuals who meet certain criteria. For example, a researcher might be interested in learning how college graduates between the ages of 20 and 35 feel about a topic. In purposive sampling, the researcher might conduct telephone interviews to intentionally seek out people who meet their criteria. Quota Sampling Quota sampling involves intentionally sampling specific proportions of each subgroup within a population. For example, political pollsters might be interested in researching the opinions of a population on a certain political issue. If they use simple random sampling, they might miss certain subsets of the population by chance. Instead, they establish criteria to assign each subgroup a certain percentage of the sample. This differs from stratified sampling because, to find individuals within each subgroup, researchers use non-random methods to fill the quotas for each subgroup. Recap Nonprobability sampling can also be used when selecting a sample in psychology research. Such methods are less representative of the general population. Techniques include convenience sampling, purposive sampling, and quota sampling. How to Conduct a Psychology Experiment Sampling Errors Sampling errors are differences between what is present in a population and what is present in a sample. Because sampling cannot include every single individual in a population, errors can occur. This can ultimately have an impact on the results of psychology research. While it is impossible to know exactly how great the difference between the population and sample may be, researchers can statistically estimate the size of the sampling errors. In political polls, for example, you might often hear of the margin of errors expressed by certain confidence levels. In general, the larger the sample size, the smaller the level of error. This is simply because the closer the sample is to the size of the total population, the more likely it is to accurately capture all of the characteristics of the population. The only way to completely eliminate sampling error is to collect data from the entire population, which is often simply too costly and time-consuming. Sampling errors can be minimized, however, by using randomized probability testing and large sample size. Summary Samples are important in psychology research because they allow scientists to study what is happening in a larger population without having to reach every individual in the entire group. Different types of samples can be used depending on what researchers are studying and the resources they have available to collect data. Probability samples tend to be more representative of the larger group. Nonprobability samples, on the other hand, tend to involve selecting participants based on availability and studying specific subsets of a larger group, which is less representative of the larger group. Sampling errors can occur, however, with any type of sampling. To minimize errors, researchers strive to use large, representative samples. What Is Reliability in Psychology? 2 Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Valliant R, Dever J. Estimating propensity adjustments for volunteer web surveys. Sociol Methods Res. 2011;40(1):105-137. doi:10.1177/0049124110392533 Lin L. Bias caused by sampling error in meta-analysis with small sample sizes. PLoS ONE. 2018;13(9):e0204056. doi:10.1371/journal.pone.0204056 Additional Reading Goodwin CJ. Research In Psychology: Methods and Design, 12th ed. John Wiley and Sons. By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book." See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Helpful Report an Error Other Submit