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Stat 226 Session Review & practice Supplemental Instruction Iowa State University population The entire group of individuals or subjects about which we want to gain information parameter A numerical “summary” describing the population of interest Leader: Luyun Course: Stat 226 Instructor: Date: 1/20/16 sample A subset of the population from which we obtain information in order to draw conclusions about the entire population statistic A numerical “ summary” describing the sample Categorical variables: Nominal: order not meaningful Ordinal: order may be meaningful Quantitative variables: take numerical values for which arithmetic operations such as adding and averaging make sense. True or False (explain): 1.) An observation in a data set refers to the observed value of a variable on a specific individual. 2.) The observed outcomes of random variables (X, Y, Z) depend on some random process and are unknown until that process occurs. 3.) “Types of stock” is an example of an ordinal, categorical variable. 4.) Inferential statistics focuses on obtaining a better understanding about the data distribution, variability, and central tendency that a variable of interest exhibits. 5.) “We can expect 25% of all ISU students to attend the season-opening football game during the 2013 season,” is an example of a descriptive statement. 6.) If we want to obtain information about the weight of all bluebirds in Iowa, collecting only the weights of bluebirds in Story County would create a representative sample. 7.) If we want to obtain information about how fast people drive on Highway 30 on the weekdays, average speed could be our variable of interest. 8.) We are interested in the average value of investment portfolios of people between the ages of 20 and 30 years old who live in the U.S. We randomly survey 400,000 of these people across the country and find that the average portfolio value is $26,000. $26,000 is the population parameter. 9.) Any numerical measure computed from a subset of the population is a summary statistic and can be observed. 1060 Hixson-Lied Student Success Center 515-294-6624 [email protected] http://www.si.iastate.edu Main Worksheet: Describing Categorical Data An email survey asks 100 soon-to-be graduates (seniors) from the ISU College of Business what color of suit they plan on wearing to the career fair this semester. (All 100 of those students plan to attend.) The resulting data can be seen in the table below. Use this data to complete the activities and answer the questions below. Color of Suit Black Brown Blue Tan Purple 1.) What is the variable of interest to this survey? 2.) Is this a categorical or quantitative variable? 3.) What is the sample? Count 74 12 10 3 1 4.) Describe the population about which we may be trying to gain information. 6.) What is the major difference between a pareto chart and a bar graph?