Can you put this in simple terms for understanding? Measuring entire populations is rarely possible in social science research. Rather, researchers study samples selected from populations. Sampling methods are techniques for selecting samples from populations. The sampling frame is a list of the population from which the sample is drawn. Probability sampling techniques are methods where the probability that a participant will be selected for inclusion in the sample is known. Random sampling is a procedure for selecting participants whereby each participant has an equal probability of being included in the sample. Random assignment of participants requires that the participants be independently assigned to groups. In systematic sampling, the population size is divided by your sample size to provide you with a number, k, for example; then, from a random starting point, you select every kth individual. For example, if your population size was 2,000 and you wanted a sample of 100, you would select every 20th individual. In stratified sampling, the population is divided into strata based on some population characteristic, and participants are randomly selected from each stratum. This ensures that each stratum is proportionally represented in the sample. Cluster sampling can be used when a population list is not available and researchers simply identify a number of clusters or groups and include all participants in the cluster in the sample. Multistage sampling is a cluster technique where smaller clusters are randomly selected from larger clusters previously randomly selected. Nonprobability sampling methods are easier to use than probability sampling methods but do not provide any way of estimating the probability that an individual in the population will be included in the sample. Convenience sampling is the term used when we select any participant who is readily available. When we choose easily available participants who fit a particular criterion, we are using quota sampling. Referral sampling involves including participants in the sample who have been referred by other participants .Recruiting participants is easy if the research is conducted on introductory psychology students and your school has a participant pool. If that's not the case, then recruitment might involve contacting family and friends or, in the case of special groups, contacting service providers. Recruitment needs to be tailored to your research and remember most IRBs need to know your recruitment strategy. Determining how many participants are needed in a sample depends on several variables, including the power of the statistic, the research design, the size of the effect, and the variability of the data.