CHAPTER 4: Data Collection and Sampling Methods to accompany Introduction to Business Statistics fourth edition, by Ronald M. Weiers Presentation by Priscilla Chaffe-Stengel Donald N. Stengel © 2002 The Wadsworth Group

Chapter 4 - Learning Objectives Describe the types of studies and their purposes: Exploratory Descriptive Causal Predictive Explain the differences between data sources: Primary Secondary: Internal versus External Differentiate between sampling designs: Probabilitistic versus nonprobabilitistic designs Differentiate between sampling and nonsampling errors. © 2002 The Wadsworth Group

Chapter 4 - Key Terms Error Types of Studies Types of Data Sampling Nonsampling Types of Studies Exploratory Descriptive Causal Predictive Types of Data Primary Secondary Internal vs External Probability sample Simple random sample Systematic sample Stratified sample Cluster sample Nonprobability sample Convenience sample Quota sample Purposive sample Judgment sample © 2002 The Wadsworth Group

Types of Studies Exploratory Descriptive Causal Predictive Understand a problem, identify relevant variables, formulate hypotheses Descriptive Establish reliable measurements Causal Determine relationships among variables Predictive Use analysis to forecast © 2002 The Wadsworth Group

Sources of Data Primary Secondary Data generated by the researcher for this study Survey, experimental, observational research most popular Tend to require more time and expense than secondary data Secondary Data gathered from another source or for another purpose Internal sources within the researcher’s organization External sources, including governmental, trade, commercial and internet sources © 2002 The Wadsworth Group

Types and Sources of Error Sampling Error Random, nondirectional When a sample is used instead of a census Nonsampling Error Directional bias overstating or understating the true population parameter Potential sources: Poor sample design Poor measurement Poor instrumentation © 2002 The Wadsworth Group

Types of Samples Simple random Systematic Probability, or Scientific, Samples: Each element to be sampled has a known (or calculable) chance of being selected. Simple random Systematic Every person has an equal chance of being selected. Best when roster of the population exists. Randomly enter a stream of elements and sample every kth element. Best when elements are randomly ordered, no cyclic variation. © 2002 The Wadsworth Group

Types of Samples Stratified Cluster Probability, or Scientific, Samples: Each element to be sampled has a known (or calculable) chance of being selected. Stratified Cluster Randomly sample elements from every layer, or stratum, of the population. Best when elements within strata are homogeneous. Randomly sample elements within some of the strata. Best when elements within strata are heterogeneous. © 2002 The Wadsworth Group

Types of Samples Convenience Quota Nonprobability Samples: Not every element has a chance to be sampled. Selection process usually involves subjectivity. Convenience Quota Elements are sampled because of ease and availability. Elements are sampled, but not randomly, from every layer, or stratum, of the population. © 2002 The Wadsworth Group

Types of Samples Purposive Judgment Nonprobability Samples: Not every element has a chance to be sampled. Selection process usually involves subjectivity. Purposive Judgment Elements are sampled because they are atypical, not representative of the population. Elements are sampled because the researcher believes the members are representative of the population. © 2002 The Wadsworth Group

Example: Types of Data Problem 4.46 The Sonic Travel Agency has not kept pace with the current boom in family vacation air travel between the agency’s northern city and sunny Florida. For each of the following, indicate whether they are primary or secondary. If secondary, further indicate whether they are internal or external. © 2002 The Wadsworth Group

Problem 4.46 a) Sonic’s research department conducts a survey of past customers to determine their level of satisfaction with the agency’s service a) Primary data The data were generated by the researcher to study this problem. © 2002 The Wadsworth Group

Problem 4.46, continued b) The Florida Bureau of Tourism sends travel agencies across the nation the results of a study describing the characteristics of winter vacationers to the state, including where and how long people intended to stay. b) Secondary data The data were not generated for the purpose of examining the question at hand. External data The data were provided by an outside agency, the Florida Bureau of Tourism. © 2002 The Wadsworth Group

Problem 4.46, continued c) To get a better grasp of the problem, the president of Sonic examines the company’s annual reports for the past ten years. c) Secondary data The data were not generated for the purpose of examining the problem at hand. Internal data The data were produced from within the firm, so they are internal data. © 2002 The Wadsworth Group

Example: Types of Studies Problem 4.48 For each of the report titles below, indicate whether the study involved was exploratory, descriptive, causal, or predictive. © 2002 The Wadsworth Group

Problem 4.48 a) “The Popularity of Bowling as a Participant Sport in Ohio.” b) “The Effects of TV Violence on Crime in Small Towns.” a) Descriptive study This is probably a descriptive study showing the number of people who bowl in Ohio. b) Causal study This is probably a causal study that examines the effect of TV violence (the cause) on crimes in small towns (the outcomes). © 2002 The Wadsworth Group

Problem 4.48, continued c) “A Preliminary Investigation of the Market for Pet Foods.” d) “Family Vacationing in the 21st Century.” c) Exploratory study This is probably an exploratory study that points out relationships and possible hypotheses for further study. d) Predictive study This is probably a predictive study to forecast vacationing patterns in the 21st century. © 2002 The Wadsworth Group

Example: Types of Errors Problem 4.64 Researchers at a university with an enrollment of 12,000 take a census of the entire student population, asking: “Shoplifting is not only illegal, it raises the prices that we all have to pay. Have you ever shoplifted from the university bookstore?” Based on this, discuss the possible presence of a) sampling and b) nonsampling error. © 2002 The Wadsworth Group

Problem 4.64 a) Sampling error not present b) Nonsampling error present a) Since the study includes the entire student population, there will be no sampling error present. b) Because the question’s wording invites biased responses, students may be afraid to admit to shoplifting, so there will be nonsampling errors present. © 2002 The Wadsworth Group