1 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman M ARIO F. T RIOLA E IGHTH E DITION E LEMENTARY S TATISTICS Chapter 2 Descriptive Statistics

2 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Chapter 2 Descriptive Statistics 2-1 Overview 2-2 Summarizing Data with Frequency Tables 2-3 Pictures of Data 2-4 Measures of Center 2-5 Measures of Variation 2-6 Measures of Position 2-7 Exploratory Data Analysis (EDA)

3 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman  Descriptive Statistics summarize or describe the important characteristics of a known set of population data  Inferential Statistics use sample data to make inferences (or generalizations) about a population 2 -1 Overview

4 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman 1. Center: A representative or average value that indicates where the middle of the data set is located 2. Variation: A measure of the amount that the values vary among themselves 3. Distribution: The nature or shape of the distribution of data (such as bell-shaped, uniform, or skewed) 4. Outliers: Sample values that lie very far away from the vast majority of other sample values 5. Time: Changing characteristics of the data over time Important Characteristics of Data

5 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman  Frequency Table lists classes (or categories) of values, along with frequencies (or counts) of the number of values that fall into each class 2-2 Summarizing Data With Frequency Tables

6 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Qwerty Keyboard Word Ratings Table

7 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Frequency Table of Qwerty Word Ratings Table RatingFrequency

8 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Frequency Table Definitions

9 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Lower Class Limits are the smallest numbers that can actually belong to different classes

10 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Lower Class Limits are the smallest numbers that can actually belong to different classes RatingFrequency

11 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Lower Class Limits Lower Class Limits RatingFrequency are the smallest numbers that can actually belong to different classes

12 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Upper Class Limits are the largest numbers that can actually belong to different classes

13 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Upper Class Limits Upper Class Limits RatingFrequency are the largest numbers that can actually belong to different classes

14 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman are the numbers used to separate classes, but without the gaps created by class limits Class Boundaries

15 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman number separating classes Class Boundaries RatingFrequency

16 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Class Boundaries Class Boundaries RatingFrequency number separating classes

17 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman midpoints of the classes Class Midpoints

18 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman midpoints of the classes Class Midpoints Class Midpoints RatingFrequency

19 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman is the difference between two consecutive lower class limits or two consecutive class boundaries Class Width

20 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Class Width RatingFrequency is the difference between two consecutive lower class limits or two consecutive class boundaries

21 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman 1. Be sure that the classes are mutually exclusive. 2. Include all classes, even if the frequency is zero. 3. Try to use the same width for all classes. 4. Select convenient numbers for class limits. 5. Use between 5 and 20 classes. 6. The sum of the class frequencies must equal the number of original data values. Guidelines For Frequency Tables

22 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman 3. Select for the first lower limit either the lowest score or a convenient value slightly less than the lowest score. 4. Add the class width to the starting point to get the second lower class limit, add the width to the second lower limit to get the third, and so on. 5. List the lower class limits in a vertical column and enter the upper class limits. 6. Represent each score by a tally mark in the appropriate class. Total tally marks to find the total frequency for each class. Constructing A Frequency Table 1. Decide on the number of classes. 2. Determine the class width by dividing the range by the number of classes (range = highest score - lowest score) and round up. class width  round up of range number of classes

23 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Figure 2-1

24 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Relative Frequency Table relative frequency = class frequency sum of all frequencies

25 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Relative Frequency Table RatingFrequency % % % % % Rating Relative Frequency 20/52 = 38.5% 14/52 = 26.9% etc. Table 2-5 Total frequency = 52

26 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Cumulative Frequency Table Cumulative Frequencies RatingFrequency Less than 320 Less than 634 Less than 949 Less than Less than Rating Cumulative Frequency Table 2-6

27 Chapter 2. Section 2-1 and 2-2. Triola, Elementary Statistics, Eighth Edition. Copyright Addison Wesley Longman Frequency Tables Rating Frequency % % % % % Rating Relative Frequency Less than 3 20 Less than 6 34 Less than 9 49 Less than Less than Rating Cumulative Frequency Table 2-6 Table 2-5 Table 2-3