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Unit 4: Sampling Design
Introduction Notes
Sampling is the process of selecting units (e.g., people, organizations) from a population of
interest so that by studying the sample we may fairly generalize our results back to the population
from which they were chosen. Each observation measures one or more properties (weight,
location, etc.) of an observable entity enumerated to distinguish objects or individuals. Survey
weights often need to be applied to the data to adjust for the sample design. Results from
probability theory and statistical theory are employed to guide practice.
4.1 Sampling – An Introduction
A sample is a part of a target population, which is carefully selected to represent the population.
Sampling frame is the list of elements from which the sample is actually drawn. Actually,
sampling frame is nothing but the correct list of population.
Example: Telephone directory, Product finder, Yellow pages.
The sampling process comprises several stages:
1. Defining the population of concern
2. Specifying a sampling frame, a set of items or events possible to measure
3. Specifying a sampling method for selecting items or events from the frame
4. Determining the sample size
5. Implementing the sampling plan
6. Sampling and data collecting
7. Reviewing the sampling process
4.1.1 Distinction between Census and Sampling
Census refers to complete inclusion of all elements in the population. A sample is a sub-group
of the population.
When is a Census Appropriate?
1. A census is appropriate if the size of population is small.
Example: A researcher may be interested in contacting firms in iron and steel or petroleum
products industry. These industries are limited in number, so a census will be suitable.
2. Sometimes, the researcher is interested in gathering information from every individual.
Example: Quality of food served in a mess.
When is Sample Appropriate?
1. When the size of population is large.
2. When time and cost are the main considerations in research.
3. If the population is homogeneous.
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