Chapter Data Collection 2 n Definitions n Level

Chapter Data Collection 2 n Definitions n Level of Measurement n Time Series and Cross-sectional Data n Sampling Concepts n Sampling Methods n Data Sources n Survey Research Mc. Graw-Hill/Irwin Copyright © 2010 by The Mc. Graw-Hill Companies, Inc. All rights reserved.

Data: Singular or Plural? Subjects, Variables, Data Sets • We will refer to Data as plural and data set as a particular collection of data as a whole. Observation – each data value. Subject (or individual) – an item for study (e. g. , an employee in your company). Variable – a characteristic about the subject or individual (e. g. , employee’s income). 2 -2

Data 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 2 -3

Level of Measurement Levels of Measurement Level of Measurement Characteristics Example Nominal Categories only Eye color (blue, brown, green, hazel) Ordinal Rank has meaning Bond ratings (Aaa, Aab, C, D, F, etc. ) Interval Distance has meaning Temperature (57 o Celsius) Ratio Meaningful zero exists Accounts payable ($21. 7 million) 2 -4

Level of Measurement Likert 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 language. ” (check one) Strongly Agree Somewhat Agree Neither Agree Nor Disagree Somewhat Disagree Strongly Disagree 2 -5

Time Series vs. Cross Sectional Data • Time Series data – data values observed over time • Cross Sectional Data – values observed at the same point in time 2 -6

Sampling Concepts • A sample involves looking only at some items selected from the population. • A census is an examination of all items in a defined population. • The target population is the population we are interested in (e. g. , U. S. gasoline prices). • The sampling frame is the group from which we take the sample (e. g. , 115, 000 stations). 2 -7

Sampling Concepts • Statistics are computed from a sample of n items, chosen from a population of N items. • Statistics can be used as estimates of parameters found in the population. • Symbols are used to represent population parameters and sample statistics. 2 -8

Sampling Methods Probability Samples Simple Random Sample Use random numbers to select items from a list (e. g. , VISA cardholders). Systematic Sample Select every kth item from a list or sequence (e. g. , restaurant customers). Stratified Sample Select randomly within defined strata (e. g. , by age, occupation, gender). Cluster Sample Like stratified sampling except strata are geographical areas (e. g. , zip codes). 2 -9

Sampling Methods Non-probability Samples Judgment Sample Use expert knowledge to choose “typical” items (e. g. , which employees to interview). Convenience Sample Use a sample that happens to be available (e. g. , ask co-worker opinions at lunch). Focus Groups In-depth dialog with a representative panel of individuals (e. g. i. Pod users). 2 -10

Sampling Methods With or Without Replacement • If we allow duplicates when sampling, then we are sampling with replacement • Duplicates are unlikely when n is much smaller than N. • If we do not allow duplicates when sampling, then we are sampling without replacement 2 -11

Data Sources • Many excellent sources are widely available. The following table summarize a few of them. 2 -12

Survey Research Basic Steps of Survey Research • Step 1: State the goals of the research. • Step 2: Develop the budget (time, money, staff). • Step 3: Create a research design (target population, frame, sample size). • Step 4: Choose a survey type and method of administration (mail, telephone, interviews, web, direct observations. 2 -13

Survey Research Basic Steps of Survey Research • Step 5: Design a data collection instrument (questionnaire). • Step 6: Pretest the survey instrument and revise as needed. • Step 7: Administer the survey (follow up if needed). • Step 8: Code the data and analyze it. 2 -14

Survey Research Survey Guidelines Planning: What is the purpose of the survey? Consider staff expertise, needed skills, degree of precision, budget. Design: Invest time and money in designing the survey. Use books and references to avoid unnecessary errors. Quality: Take care in preparing a quality survey so that people will take you seriously. 2 -15

Survey Research Survey Guidelines Pilot Test: Pretest on friends or co-workers to make sure the survey is clear. Buy-in: Improve response rates by stating the purpose of the survey, offering a token of appreciation or paving the way with endorsements. Expertise: Work with a consultant early on. 2 -16

Survey Research Questionnaire Design • Use a lot of white space in layout. • Begin with short, clear instructions. • State the survey purpose. • Assure anonymity. • Instruct on how to submit the completed survey. 2 -17

Survey Research Questionnaire 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. 2 -18