What is a Sampling Frame?
Watch the video for an overview and examples, or read on below:
A sampling frame is a list of all the items in your population. It’s a complete list of everyone or everything you want to study. The difference between a population and a sampling frame is that the population is general and the frame is specific. For example, the population could be “People who live in Jacksonville, Florida.” The frame would name all of those people, from Adrian Abba to Felicity Zappa. A couple more examples:
Population: People in STAT101.
Sampling Frame: Adrian, Anna, Bob, Billy, Howie, Jess, Jin, Kate, Kaley, Lin, Manuel, Norah, Paul, Roger, Stu, Tim, Vanessa, Yasmin.
Population: Birds that are pink.
Sampling Frame:
- Brown-capped Rosy-Finch.
- White-winged Crossbill.
- American Flamingo.
- Roseate Spoonbill.
- Black Rosy-Finch.
- Cassin’s Finch.
When you draw a sample in statistics, you need a list of items to draw the sample from. Take a very simple population: bingo balls numbered 1 to 99. Your frame would be a list of all those balls: 1 , 2, 3…99. Once you have your list, you can go ahead and draw your sample.
A sampling frame can be a list of just about anything. For example, the population could be “All infectious diseases in the United States.” The frame is below:
Qualities of a Good Sampling Frame
You can’t just use any list you come across! Care must be taken to make sure your sampling frame is adequate for your needs. For example, according to Alaska University, a good sample frame for a project on living conditions would:
- Include all individuals in the target population.
- Exclude all individuals not in the target population.
- Includes accurate information that can be used to contact selected individuals.
Other general factors that you would want to make sure you have:
- A unique identifier for each member. This could be a simple numerical identifier (e.g. from 1 to 1000). Check to make sure there are no duplicates in the frame.
- A logical organization to the list. For example, put them in alphabetical order.
- Up to date information. This may need to be periodically checked (e.g. for address changes).
In some cases, it might be impossible, or very difficult, to get a sampling frame. For example, getting a list of prostitutes in your city isn’t likely (mostly because of the fact that most prostitutes won’t want to be found). Sometimes, techniques like snowball sampling must be used to make up for the lack of sampling frame. Snowball sampling is where you find one person (or a few people) for your survey or experiment. You then ask them to find someone else who would be willing to participate. Then that person finds someone else, and so on, until you have enough people for your needs.
Sampling Frame vs. Sample Space
A sampling frame is a list of things that you draw a sample from. A sample space is a list of all possible outcomes for an experiment. For example, you might have a sampling frame of names of people in a certain town for a survey you’re going to be conducting on family size. The sample space is all possible outcomes from your survey: 1 person, 2 people, 3 people…10 or more.
References
Agresti A. (1990) Categorical Data Analysis. John Wiley and Sons, New York.
Everitt, B. S.; Skrondal, A. (2010), The Cambridge Dictionary of Statistics, Cambridge University Press.
Gonick, L. (1993). The Cartoon Guide to Statistics. HarperPerennial.
Kotz, S.; et al., eds. (2006), Encyclopedia of Statistical Sciences, Wiley.