Chapter 2.3（课件）- 《统计学基础（英文版）》同步教学（人民大学版）

Chapter Descriptive Statistics 2 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. 1 Larson/Farber 6th ed Chapter 1 Chapter Outline 2.1 Frequency Distributions and Their Graphs 2.2 More Graphs and Displays 2.3 Measures of Central Tendency 2.4 Measures of Variation 2.5 Measures of Position 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Section 2.3 Measures of Central Tendency . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Section 2.3 Objectives How to find the mean, median, and mode of a population and of a sample How to find the weighted mean of a data set, and how to estimate the sample mean of grouped data How to describe the shape of a distribution as symmetric, uniform, or skewed and how to compare the mean and median for each . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Measures of Central Tendency Measure of central tendency A value that represents a typical, or central, entry of a data set. Most common measures of central tendency: Mean Median Mode . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Measure of Central Tendency: Mean Mean (average) The sum of all the data entries divided by the number of entries. Sigma notation: Σx = add all of the data entries (x) in the data set. Population mean: Sample mean: . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Example: Finding a Sample Mean The weights (in pounds) for a sample of adults before starting a weight-loss study are listed. What is the mean weight of the adults? 274 235 223 268 290 285 235 . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Solution: Finding a Sample Mean The sum of the weights is Σx = 274 + 235 + 223 + 268 + 290 + 285 + 235 = 1810 To find the mean weight, divide the sum of the weights by the number of adults in the sample. The mean weight of the adults is about 258.6 pounds. . = 274 235 223 268 290 285 235 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Measure of Central Tendency: Median Median Th