Chap007 Sampling aa

8/13/2019 Chap007 Sampling aa

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Chapter 7: SAMPLING


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Learning Objectives

Explain the role of sampling in the research processDistinguish between probability andnonprobability samplingUnderstand the factors to consider whendetermining sample sizeUnderstand the steps in developing asampling plan


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The Future of Mobile Search


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Sampling

Sampling is the process of selecting a smallnumber of elements from a larger definedtarget group of elements such that the

information gathered from the small groupwill allow judgments to be made about thelarger groups


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Census


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Sources of Error

Sampling error is any type of bias that isattributable to mistakes in either drawing asample or determining the sample size

Nonsampling error is bias that occurs in aresearch study regardless of whether asample or census is used, such as bias caused

by measurement error, response errors, orcoding errors


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Sampling Methods

Probabilitysampling

Nonprobabilitysampling


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Types of Sampling Methods

ProbabilitySimple randomsampling

Systematic randomsamplingStratified random

samplingCluster sampling

NonprobabilityConvenience samplingJudgment samplingQuota samplingSnowball sampling


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Forms of Probability Sampling_1

Simple random sampling is a method of probability sampling in which every unit hasan equal nonzero chance of being selected

Systematic random sampling is a method of probability sampling in which the definedtarget population is ordered and the sample is

selected according to position using a skipinterval


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Steps in Drawing aSystematic Random Sample

1: Obtain a list of units that contains anacceptable frame of the target population2: Determine the number of units in the listand the desired sample size3: Compute the skip interval4: Determine a random start point5: Beginning at the start point, select the units

by choosing each unit that corresponds to theskip interval


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Skip interval

Skip interval = defined target pop list size /desired sample sizeIn a systematic sampling study, if thesampling frame has 6,000 names and thedesired sample size is 200, the "skip interval"should be______:


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Steps in Drawing aStratified Random Sample

1: Divide the target population intohomogeneous subgroups or strata2: Draw random samples from each stratum3: Combine the samples from each stratuminto a single sample of the target population


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Nonprobability Sampling Methods

Convenience sampling reliesupon convenience and access

Judgment sampling relies upon beliefthat participants fit characteristics

Quota sampling emphasizes representationof specific characteristics

Snowball sampling relies upon respondentreferrals of others with like characteristics


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Factors to Consider in Sample Design

Research objectives Degree of accuracy

Resources Time frame

Knowledge of target population Research scope

Statistical analysis needs


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Factors AffectingSample Size for Probability Designs

Variability of the population characteristicunder investigationLevel of confidence desired in the estimateDegree of precision desired in estimating the

population characteristic


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Probability Sampling and Sample Sizes

When estimating a population meann = (Z2B,CL)( 2/e2)

When estimates of a population proportionare of concern

n = (Z2B,CL)([P x Q]/e2)


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If the estimated population standard deviation based on previous studies is $40, and theacceptable error is plus or minus $4, and the

z-value for a 95 percent level of confidence is1.96, What is the needed sample size ?


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Problems

If the estimated population proportion is .40 based on previous studies, and the acceptableerror is plus or minus 4 percent, and the z-

value for a 95 percent level of confidence is1.96, what is the needed sample size ?


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Problem 2

In order to determine the proportion of people who favor imposing sales tax for allInternet purchases, What is the minimum

sample size needed for a precision level of 5 percent and a confidence level of 95 percent?


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1. Define the Target Population

2. Select the Data Collection Method

3. Identify the Sampling Frame(s) Needed

4. Identify the Appropriate Sampling Method

5. Determine Sample Sizes and Contact Rates

6. Create Plan for Selecting Sampling Units

7. Execute the Operational Plan

Steps in Developing a Sampling Plan


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Marketing Research in Action:Santa Fes New Menu

How should participants be selected? What isthe ideal sampling design?How many new menu items can be examinedon the survey?How should the survey be administered?

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Chap007 Sampling aa