Sampling

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.

Click on the links below to read 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