Imagine you are the program director of a national program across all 50 states serving at-risk youth. In total, your program serves over 10,000 students at 325 middle schools. You want to know how well the program is working to improve students’ perception of school safety. However, you have limited time, resources, and funding for implementing an evaluation. An alternative to surveying every program participant is to select a sample of participants to survey.
Quick Facts About Sampling
- A Sampling method is typically used when an entire target population is too large or it is not feasible to collect data from the group due to geographic distance, funding, etc.
- Consists of selecting individuals from a target population
- Enables evaluators to generalize results about the population being studied
If you choose to use a sampling procedure, the selection should be based on the purpose of your evaluation. Depending on the goals of your evaluation, unbiased sampling (such as systematic sampling) or less rigorous techniques (such as snowball sampling) might be most appropriate.
See the following to learn more about sampling types:
Types of Sampling
| | Definition | Uses | Example |
| Random Sampling | All members of a population have an equal probability of being selected for the sample | When looking for an unbiased sample that is representative of the population | Drawing, at random, the first 100 names out of a hat from your total population |
| Systematic Sampling | Type of random sampling where every nth member from a population is selected into the sample | When looking for a fairly representative population | In a sample of underserved youth, selecting every 7th person of your target population |
| Convenience Sampling | Selection is nonrandom and participants are selected based on ease of access | When collecting general information about the population you intend to sample while keeping costs at a minimum | Interviewing the first 6 people you see in the morning or the first 4 people you talk to tomorrow |
| Snowball Sampling | Having participants refer or recommend other potential participants | When the population being sampled is not readily available or difficult to find | An evaluator trying to gather information about homeless individuals asks participants to refer them to someone else they might know in the same situation |
| Intensity Sampling | Involves measuring extreme populations | When trying to understand a phenomenon | Selecting a population of geniuses or a population of college students with extremely low grade point averages |