Lecture Marketing research - Chapter 10: Basic sampling issues

After studying this chapter you will be able to: Understand the concept of sampling, learn the steps in developing a sampling plan, understand the concepts of sampling error and nonsampling error, understand the differences between probability samples, and nonprobability samples, understand sampling implications of surveying over the Internet.

Learning Objectives

Copyright © 2004 John Wiley & Sons, Inc.

1 To understand the concept of sampling.

2 To learn the steps in developing a sampling plan.

3 To understand the concepts of sampling error

and nonsampling error.

4 To understand the differences between

probability samples, and nonprobability

samples.

5 To understand sampling implications of

surveying over the Internet.

Learning Objectives

Sampling Defined:

1 The process of obtaining information from a subset of

a larger group

2 A market researcher takes the results from the

sample to make estimates of the larger group

3 Sampling a small percentage of a population can

result in very accurate estimates

To understand the concept of sampling.

The Concept of Sampling

Population or Universe

1 The population or population of interest is the total

group of people from whom information is needed

2 Defining the population of interest is the first step in

the sampling process

3 Requires good logic and judgment

4 Based on the characteristics of current or target

customer

Sample versus Census

Census: Data about every member of the population.

Sample: A subset of the population

Definition Of Important

Learning Objectives

Step1.

Define the Population of Interest

Step 2 Choose Data Collection Method

Step 3.

Choose Sampling Frame

(4) Select a Sampling Method

Step 5

Determine Sample Size

Step 6 Develop

Operational Plan

Step 7.

Execute Operational Plan

Step One: Defining the Population of Interest

Specifying the characteristics from whom information is needed

Define the characteristics of those that should be

excluded

Step Two: Choose Data Collection Method

Impacts for the sampling process

Step Three: Choosing Sampling Frame

A list of elements or members from which we select units

Learning Objectives

Step Four: Select a Sampling Method

The selection will depend on:

• The objectives of the study

• The financial resources available

• Time limitations

• The nature of the problem

Probability Samples

A known, nonzero probability of selection

To learn the steps in developing a sample plan.

Steps In Developing A

Sampling Plan

Nonprobability Samples

Elements selected in a nonrandom manner

1 Nonrandomness—selected on the basis of

Learning Objectives

Advantages Of Probability Samples

1 Information from a representative cross-section

2 Sampling error can be computed

3 Results are projectable to the total population

Disadvantages Of Probability Samples

1 More expansive than nonprobabiity samples

2 Take more time to design and execute

To understand the steps in developing a sample plan.

Steps In Developing A

Sampling Plan

Disadvantages of Nonprobability Samples

1 Sampling error cannot be computed

2 Representativeness of the sample is not known

3 Results cannot be projected to the population

Advantages of Nonprobability Samples

1 Cost less than probability

2 Can be conducted more quickly

3 Produces samples that are reasonably

Learning Objectives

Sampling methods

Probability samples

Step Five: Determine Sample Size

• Discussed more in depth in Chapter 11

Learning Objectives

Step Six: Develop of Operational Procedures for

Selecting Sample Elements

Specify whether a probability or nonprobability sample is being used

Step Seven: Execution the Sampling Plan

The final step of the operational sampling plan

Include adequate checking of specified procedures

To distinguish between probability samples and nonprobability samples.

Steps In Developing A

Sampling Plan

Sampling Error

The error that results when the same sample is not perfectly representative of the population

Two types of sampling error:

sampling error and nonsampling error.

• Random error: due to chance and cannot be avoided

Measurement or Nonsampling Error

Includes everything other than sampling error that can

cause inaccuracy and bias

To understand the concepts of sampling error and nonsampling error.

Sampling And

Nonsampling Errors

Simple Random Sampling

The purest form of probability sample

probability and nonprobability sampling methods.

Probability of Selection = Sample Size

Learning Objectives

Stratified Samples

Probability samples that are distinguished by the following steps:

1 The original population is divided into two or more

mutually exclusive and exhaustive subsets

2 Simple random samples of elements from the two or

more subsets are chosen independently from each other

To understand the differences in probability and nonprobability sampling methods.

Probability Sampling

Methods

Three steps: In implementing a properly stratified sample:

1 Identify salient demographic or classification factors

correlated with the behavior of interest

2 Determine what proportions of the population fall into

various sub subgroups under each stratum

• proportional allocation

• disproportional or optimal allocation

3 Select separate simple random samples from each

Learning Objectives

Cluster Samples

Sampling units are selected in groups

1 The population of interest is divided into mutually

exclusive and exhaustive subsets

2 A random sample of the subsets is selected

• One-stage cluster—all elements in subset

selected

• Two-stage cluster—elements selected in some

probabilistic manner from the selected subsets

To understand the differences in probability and nonprobability sampling methods.

Probability Sampling

Methods

probability and nonprobability sampling methods.

Learning Objectives

To understand sampling implications

of surveying over the Internet.

Advantages of Internet sampling:

• Target respondents can complete the survey at their

convenience

• Data collection is inexpensive

• The interview can be administered under software control

• The survey can be completed quickly

Internet Sampling

Disadvantages of Internet Interviewing

1 users of the internet are not representative of the

general population

2 no comprehensive and reliable source of email

addresses exists

To understand sampling implications

of surveying over the Internet.

Internet Sampling

Learning Objectives

• The Concept of Sampling

• Definition Of Important Terms

• Steps In Developing A Sampling Plan

• Sampling And Nonsampling Errors

• Probability Sampling Methods

• Nonprobability Sampling Methods

• Sampling Over the Internet

SUMMARY

The End

Copyright © 2004 John Wiley & Sons, Inc.