Chapter 2


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CHAPTER 2: COLLECTING DATA 2.1 INTRODUCTION Once the objectives of the statistical study have been determined, the variables of interest have been defined, and the population and its sample have been identified and fully described, which is Step 1 in learning from data; we must select the most appropriate method to collect the data. Generally, we can obtain the data in two major different ways: Secondary source data and primary source data . 2.1.1 SECONDARY SOURCE DATA Secondary source data refer to the data that have been gathered by someone other than the researcher for some other purpose and are available in an existing source . Existing sources for secondary source data include: book, journal, newspaper, business records, government records, or internet –website. The most comprehensive existing source for secondary source data is a census . DEFINITION 2.1: CENSUS A census is the process of measuring a variable for every member of a population along with obtaining information about certain characteristics of each member. The United States conducts a census every 10 years in order to learn the demographic make-up of the United States. Everyone whose usual residence is within the United States borders must fill out a questionnaire packet. Taking a census provides complete information about the population of interest, but it is often very costly and extremely difficult to perform. 2.1.2 PRIMARY SOURCE DATA Primary source data refer to the data generated by a researcher for the specific problem or decision at hand. The researcher collects data from either an experimental study or an observational study . Section 2.3 gives further details about these two common sources of data. 2.2 DEFINITIONS OF BASIC TERMS USED DEFINITION 2.2: DESIGN A design refers to the method used to choose the sample from the population. DEFINITION 2.3: TREATMENT A treatment is a specific regimen or procedure assigned to participants by the experimenter. Dr. LOHAKA – QBA 2302 Chapter 2: COLLECTING DATA Page 19
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NOTE 2.1 In data analysis, the treatment can be considered as an explanatory variable since it is controlled by the researcher and we wish to see if it can explain some kind of reaction in the experimental unit. The variable measured to judge the reaction is called the response . DEFINITION 2.4: TREATMENT GROUP A treatment group is a group of experimental units receiving the active treatment. DEFINITION 2.5: PLACEBO A placebo is a pill (such as sugar pill) or treatment designed to look just like the active treatment but with no active ingredients that is given to the experimental units in the control group which (hopefully) prevents them from knowing if they received the treatment or not. DEFINITION 2.6:
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