Data CollectionData Collection Definitions Level of Measurement Time Series and Cross-sectional Data Sampling Concepts Sampling Methods Data Sources Survey Research

Chapter2222

Copyright © 2010 by The McGraw-Hill Companies, Inc. All rights reserved.

McGraw-Hill/Irwin

Data: Singular or Plural?Data: Singular or Plural?

Subjects, Variables, Data Sets

• We will refer to DataData as plural and data setdata set as a particular collection of data as a whole.

ObservationObservation – each data value.

SubjectSubject (or individual) – an item for study (e.g., an employee in your company).

VariableVariable – a characteristic about the subject or individual (e.g., employee’s income).

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Data DefinitionsData Definitions

• Categorical or Qualitative – data values which are non-numeric

• Numerical or quantitative – data values which are numeric

• Data Coding – done to simplify the data when the exact data magnitude is of little interest

• Binary Data – data values with only two values, indicating the presence (1) or the absence (0) of a characteristic of interest

• Discrete Data – data values which arise from counting• Continuous Data – numerical values which lie within an interval

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Level of MeasurementLevel of Measurement

Levels of MeasurementLevels of Measurement

Level of Level of MeasurementMeasurement CharacteristicsCharacteristics ExampleExample

NominalNominal Categories only Eye color ((blueblue, , brownbrown, , greengreen, , hazelhazel))

OrdinalOrdinal Rank has meaning Bond ratings (Aaa, Aab, C, D, F, etc.)

IntervalInterval Distance has meaning Temperature (57o Celsius)

RatioRatio Meaningful zero exists Accounts payable ($21.7 million)

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Level of MeasurementLevel of Measurement

Likert ScalesLikert Scales A special case of interval data frequently used in

survey research. The coarseness of a Likert scale refers to the

number of scale points (typically 5 or 7).

““College-bound high school students should be required to study a foreign College-bound high school students should be required to study a foreign language.” (check one)language.” (check one)

StronglyStronglyAgreeAgree

SomewhatSomewhatAgreeAgree

Neither AgreeNeither AgreeNor DisagreeNor Disagree

SomewhatSomewhatDisagreeDisagree

StronglyStronglyDisagreeDisagree

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Time Series vs. Cross Sectional DataTime Series vs. Cross Sectional Data

•Time Series data – data values observed over time

• Cross Sectional Data – values observed at the same point in time

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Sampling ConceptsSampling Concepts

• A samplesample involves looking only at some items selected from the population.

• A censuscensus is an examination of all items in a defined population.

• The target populationtarget population is the population we are interested in (e.g., U.S. gasoline prices).

• The sampling framesampling frame is the group from which we take the sample (e.g., 115,000 stations).

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Sampling ConceptsSampling Concepts

• StatisticsStatistics are computed from a sample of n items, chosen from a population of N items.

• Statistics can be used as estimates of parametersparameters found in the population.

• Symbols are used to represent population parameters and sample statistics.

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Sampling MethodsSampling Methods

Probability SamplesProbability Samples

Simple Random SampleSimple Random Sample Use random numbers to select items from a list (e.g., VISA cardholders).

Systematic SampleSystematic Sample Select every kth item from a list or sequence (e.g., restaurant customers).

Stratified SampleStratified Sample Select randomly within defined strata (e.g., by age, occupation, gender).

Cluster SampleCluster Sample Like stratified sampling except strata are geographical areas (e.g., zip codes).

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Sampling MethodsSampling Methods

Non-probability SamplesNon-probability SamplesJudgment SampleJudgment Sample Use expert knowledge to choose “typical” items

(e.g., which employees to interview).

Convenience Convenience SampleSample

Use a sample that happens to be available (e.g., ask co-worker opinions at lunch).

Focus GroupsFocus Groups In-depth dialog with a representative panel of individuals (e.g. iPod users).

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Sampling MethodsSampling Methods

With or Without ReplacementWith or Without Replacement• If we allow duplicates when sampling, then we

are sampling with replacementwith replacement.

• Duplicates are unlikely when n is much smaller than N.

• If we do not allow duplicates when sampling, then we are sampling without replacementwithout replacement.

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Data SourcesData Sources

• Many excellent sources are widely available. The following table summarize a few of them.

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• Step 1: State the goals of the research.Step 1: State the goals of the research.

• Step 2: Develop the budget (time, money, staff).Step 2: Develop the budget (time, money, staff).

• Step 3: Create a research design (target population, Step 3: Create a research design (target population, frame, sample size). frame, sample size).

• Step 4: Choose a survey type and method ofStep 4: Choose a survey type and method of administration (mail, telephone, interviews, web, administration (mail, telephone, interviews, web,

direct observations.direct observations.

Basic Steps of Survey ResearchBasic Steps of Survey Research

Survey ResearchSurvey Research

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• Step 5: Design a data collection instrumentStep 5: Design a data collection instrument (questionnaire). (questionnaire).

• Step 6: Pretest the survey instrument and revise asStep 6: Pretest the survey instrument and revise as needed. needed.

• Step 7: Administer the survey (follow up if needed).Step 7: Administer the survey (follow up if needed).

• Step 8: Code the data and analyze it.Step 8: Code the data and analyze it.

Basic Steps of Survey ResearchBasic Steps of Survey Research

Survey ResearchSurvey Research

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Survey GuidelinesSurvey Guidelines

Survey ResearchSurvey Research

PlanningPlanning:: What is the purpose of the survey? What is the purpose of the survey? Consider staff expertise, needed skills, degree of Consider staff expertise, needed skills, degree of precision, budget.precision, budget.

DesignDesign: : Invest time and money in Invest time and money in designing the survey. Use books and designing the survey. Use books and references to avoid unnecessary errorsreferences to avoid unnecessary errors..

QualityQuality: : Take care in preparing a quality Take care in preparing a quality survey so that people will take you survey so that people will take you seriously.seriously.

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Survey ResearchSurvey Research

Survey GuidelinesSurvey Guidelines Pilot TestPilot Test: : Pretest on friends or co-workers to make Pretest on friends or co-workers to make

sure the survey is clear.sure the survey is clear.

Buy-inBuy-in:: Improve response rates by stating the Improve response rates by stating the purpose of the survey, offering a token of purpose of the survey, offering a token of appreciation or paving the way with endorsements.appreciation or paving the way with endorsements.

ExpertiseExpertise: : Work with a consultant early on.Work with a consultant early on.

Questionnaire DesignQuestionnaire Design

• Instruct on how to submit the completed survey.

• Use a lot of white space in layout.

• Begin with short, clear instructions.

• State the survey purpose.

• Assure anonymity.

Survey ResearchSurvey Research

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Questionnaire DesignQuestionnaire Design• Break survey into naturally occurring sections.

• Let respondents bypass sections that are not applicable (e.g., “if you answered no to question 7, skip directly to Question 15”).

• Pretest and revise as needed.

• Keep as short as possible.

Survey ResearchSurvey Research

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