The post is about the concept of Sampling Frame and Sampling Unit.
Table of Contents
Sampling Unit
The population divided into a finite number of distinct and identifiable units is called sampling units. OR
The individuals whose characteristics are to be measured in the analysis are called elementary or sampling units. OR
Before selecting the sample, the population must be divided into parts called sampling units or simply sample units.
Sampling Frame
The list of all the sampling units with a proper identification (which represents the population to be covered is called the sampling-frame). The frame may consist of either a list of units or a map of the area (in case a sample of the area is being taken), such that every element in the population belongs to one and only one unit.
The frame should be accurate, free from omission and duplication (overlapping), adequate, and up-to-date units must cover the whole of the population and should be well identified.
In improving the sampling design, supplementary information for the field covered by the sampling frame may also be valuable.
Sampling Frame and Sampling Unit: Examples
- List of households (and persons) enumerated in the population census.
- A map of areas of a country showing the boundaries of area units.
- In sampling an agricultural crop, the unit might be a field, a farm, or an area of land whose shape and dimensions are at our disposal.
An ideal sampling frame will have the following qualities/characteristics:
- all sampling units have a logical and numerical identifier
- all sampling units can be found i.e. contact information, map location, or other relevant information about sampling units is present
- the frame is organized in a logical and systematic manner
- the sampling frame has some additional information about the units that allow the use of more advanced sampling frames
- every element of the population of interest is present in the frame
- every element of the population is present only once in the frame
- no elements from outside the population of interest are present in the frame
- the data is up-to-date
Classification of Sampling Frame
A sampling frame can be classified as subject to several types of defects as follows:
A frame may be inaccurate: where some of the sampling units of the population are listed inaccurately or some units that do not exist are included in the list.
A frame may be inadequate: when it does not include all classes of the population that are to be taken in the survey.
A frame may be incomplete: when some of the sampling units of the population are either completely omitted or include more than once.
A frame may be out of date: when it has not been updated according to the demand of the occasion, although it was accurate, complete, and adequate at the time of construction.
Imagine you are interested in studying the eating habits of people in your city. The entire population of the city would be too big to survey, so you decide to take a sample. The sampling-frame would be like a phone book of everyone in the city. The sampling unit would be each person listed in the phone book.
Summary
Remember that the quality of the sampling-frame directly affects the representativeness of the sample. If the frame does not accurately reflect the population, the results may be biased.
In short, the quality of the sampling-frame directly affects the validity of the study. Ideally, the frame should be complete (including everyone in the target population) and accurate (with no duplicates or errors). In reality, perfect frames can be difficult to achieve, but researchers strive to get as close as possible.
FAQs about Samling Frames and Sampling Units
- Define Sampling frame.
- Define Sampling unit.
- How a sampling frame should be?
- What is the classification of the sampling frame?
- Give some examples of sampling frames and sampling units.
