Charts and Graphs Chapter 2 MSIS 111 Prof. Nick Dedeke
Objectives • Understanding data presentation • Discrete versus continuous data Differentiate between grouped and ungrouped data • Construct frequency distributions • Construct histogram, frequency polygon and other charts
Types of Variables • Discrete variables have parameters that are whole numbers only, e.g. 3 cars, 5 cars, 6 cars , 7 cars, 9 cars, 11 cars • Continuous variables have parameters that allow both whole numbers and decimal numbers, e.g. $ 1.2, $ 1.4, $ 4.2
Exercise: Using Frequency Distribution for Discrete Data • What is the average of these dimension data (all observations number of houses)?1,1,1,1,1,1,1,12,2,2,2,2,2,2,24,4,5,5,6,6,8,89,9,9, 10,10,10,10,10,1011,11,11
Data Presentation • One of the characteristics of good statistics is the fact that everyone uses the same approach to organize data. • The approaches used are called tools of descriptive statistics
Problem: Frequency Distribution for Continuous Data • What is the average of these continuous data (all observations in inches)?1.6,1.5,1.2,1.4,1.6,1.2,1.6,1.62.1,2.7,2.3,2.5,2.8,2.9,2.8,2.94.2,4.6,5.2,5.4,6.1,6.5,,7.6,8.3,8.69.6,9.1,9.6,10.0,10.5,10.6,10.8,10.3,10.4,11.8,11.8,11.8, 12.3,12.4,12.5
Exercise: Frequency Distribution for Continuous Data • Range = Largest – Smallest number = 12.5 – 1.2 = 11.3Set number of classes to use to group data = 6 classesClass width = 11.3/6 = 1.88 or 2Class width of 2 means that one builds classes where the difference between the highest and lowest number in each class is 2
Class Width $650 $750 $700 Lowercutpoint Uppercutpoint Midpoint
Exercise: Frequency Distribution for Grouped Data
Types of Charts:Pie Charts
Types of Charts: Oglive
Types of Charts: Histograms
Graph: Box-plots IQR • Vertical line in box represents median • Left end of box depicts the 25th percentile (1st quartile) • Right end of box depicts the 75th percentile (2nd quartile) • Horizontal line from each end of box are drawn to the most extreme data points (only those no farther than 1.5 Inter quartile range (IQR)) 1Q 2Q 3Q 4Q 75th percentile 25th percentile 50th percentile
Graph: Box-plots vs. Histograms 1Q 2Q 3Q 4Q • Vertical line in box represents median • Left end of box depicts the 25th percentile (1st quartile) • Right end of box depicts the 75th percentile (2nd quartile) • Horizontal line from each end of box are drawn to the most extreme data points ( no farther than 1.5 Inter quartile range (IQR) 25thpercentile 75th percentile 50th percentile Frequency 1Q 2Q 3Q 4Q X Median
Simulations • Box plots vs. histograms • Hints • Match extreme values • Match the length of the inter quartile range or the middle 50% of the data to histogram • Use the pattern of the data to visualize the position of the median • Median moves forward • Median moves backwards
