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§ 1.3 EXPERIMENTAL DESIGN

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2 DESIGNING A STATISTICAL STUDY GUIDELINES 1.Identify the variable(s) of interest (the focus) and the population of the study. 2.Develop a detailed plan for collecting data. If you use a sample, make sure the sample is representative of the population. 3.Collect the data. 4.Describe the data, using descriptive statistics techniques. 5.Interpret the data and make decisions about the population using inferential statistics. 6.Identify any possible errors.

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3 METHODS OF DATA COLLECTION In an observational study, a researcher observes and measures characteristics of interest of part of a population. In an experiment, a treatment is applied to part of a population, and responses are observed. A simulation is the use of a mathematical or physical model to reproduce the conditions of a situation or process. A survey is an investigation of one or more characteristics of a population. A census is a measurement of an entire population. A sampling is a measurement of part of a population.

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4 IDENTIFYING THE DATA COLLECTION METHOD What method of data collection would you use to collect data for a study where you would like to determine the chance of getting three girls in a family of three children? A.Take a census B.Use a simulation C.Perform an experiment D.Use sampling

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5 IDENTIFYING THE DATA COLLECTION METHOD What method of data collection would you use to collect data for a study where a drug was given to 10 patients and a placebo to another group of 10 patients to determine if the drug has an effect on a patient’s illness? A.Take a census B.Use a simulation C.Perform an experiment D.Use sampling

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6 IDENTIFYING THE DATA COLLECTION METHOD What method of data collection would you use to collect data for a study of the salaries of college professors at Lackawanna College? (Note: There are approximately 40 professors at L.C.) A.Take a census B.Use a simulation C.Perform an experiment D.Use sampling

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7 STRATIFIED SAMPLES A stratified sample has members from each segment of a population. This ensures that each segment from the population is represented. Freshmen SophomoresJuniorsSeniors

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8 CLUSTER SAMPLES A cluster sample has all members from randomly selected segments of a population. This is used when the population falls into naturally occurring subgroups. The city of Clarksville divided into city blocks. All members in each selected group are used.

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9 SYSTEMATIC SAMPLES A systematic sample is a sample in which each member of the population is assigned a number. A starting number is randomly selected and sample members are selected at regular intervals. Every fourth member is chosen.

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10 CONVENIENCE SAMPLES A convenience sample consists only of available members of the population.

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11 IDENTIFYING THE SAMPLING TECHNIQUE Example: You are doing a study to determine the number of years of education each teacher at your college has. Identify the sampling technique used if you select the samples listed. 1.) You randomly select two different departments and survey each teacher in those departments. A.Stratified Sample B.Cluster Sample C.Systematic Sample D.Convenience Sample

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12 IDENTIFYING THE SAMPLING TECHNIQUE Example: You are doing a study to determine the number of years of education each teacher at your college has. Identify the sampling technique used if you select the samples listed. 2.) You select only the teachers you currently have this semester. A.Stratified Sample B.Cluster Sample C.Systematic Sample D.Convenience Sample

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13 IDENTIFYING THE SAMPLING TECHNIQUE Example: You are doing a study to determine the number of years of education each teacher at your college has. Identify the sampling technique used if you select the samples listed. 3.) You divide the teachers up according to their department and then choose and survey some teachers in each department. A.Stratified Sample B.Cluster Sample C.Systematic Sample D.Convenience Sample

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14 IDENTIFYING THE SAMPLING TECHNIQUE At a local community college, five statistics classes are randomly selected and all of the students from each class are interviewed. A.Stratified B.Cluster C.Systematic D.Convenience E.Random

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15 IDENTIFYING THE SAMPLING TECHNIQUE A Marywood University student interviews everyone in his statistics class to determine who owns a car. A.Stratified B.Cluster C.Systematic D.Convenience E.Random

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16 IDENTIFYING THE SAMPLING TECHNIQUE Based on 8,000 responses from 32,500 questionnaires sent to its alumni, a major university estimated that the annual salary of its alumni was $103,000 per year. A.Stratified B.Cluster C.Systematic D.Convenience E.Random

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17 IDENTIFYING THE SAMPLING TECHNIQUE A market researcher randomly selects 500 drivers under 35 year of age and 300 drivers over the age of 35 to test a new car design. A.Stratified B.Cluster C.Systematic D.Convenience E.Random

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