Graphing and Introduction to Statistics Chapter Eight

Reading Pictographs, Bar Graphs, Histograms, and Line Graphs Section 8.1

Pictographs A pictograph is a graph in which pictures or symbols are used. This type of graph contains a key that explains the meaning of the symbol used. An advantage of using a pictograph to display information is that comparisons can easily be made. A disadvantage of using a pictograph is that it is often hard to tell what fractional part of a symbol is shown. 3 Martin-Gay, Prealgebra, 5ed

The pictograph shows the approximate number of passengers traveling on the leading U.S. passenger airlines. Delta United American Southwest US Airways Northwest = 25 million passengers Leading U.S. Passenger Airlines Source: Air Transport Association of America

Bar Graphs Bar graphs can appear with vertical bars or horizontal bars. An advantage to using bar graphs is that a scale is usually included for greater accuracy. 5 Martin-Gay, Prealgebra, 5ed

The bar graph shows the population of the world’s largest cities. Source: United Nations, Dept. for Economic and Social Information and Policy Analysis 6 Bar Graphs Martin-Gay, Prealgebra, 5ed

Histograms A histogram is a special bar graph. The width of each bar represents a range of numbers called a class interval. The height of each bar corresponds to how many times a number in the class interval occurred and is called the class frequency. The bars in a histogram lie side by side with no space between them. 7 Martin-Gay, Prealgebra, 5ed

Histograms The test scores of 36 students are summarized in the table Student Scores Frequency (# of students) 8

Line Graphs Another common way to display information graphically is by using a line graph. An advantage of a line graph is that it can be used to visualize relationships between two quantities. A line graph can also be very useful in showing change over time. 9 Martin-Gay, Prealgebra, 5ed

Line Graphs Source: Storm Prediction Center Tornado Deaths Jan. Feb. March April May June July August Sept. Oct. Nov. Dec. Average Number of U.S. Deaths ( ) 10