2.2 bar graphs, circle graphs, and time series graphs
2.2 Bar Graphs, CircleGraphs, and Time-Series Graphs CHAPTER 2 ORGANIZING DATA
Page 55 Bar Graphs A bar graph can be used to display quantitative or qualitative data. A clustered bar graph has two (or more) bars for each class Features of a Bar Graph Bars can be vertical or horizontal Bars have the same width and there is the same amount of space between bars The lengths of the bars represent values of the variable being displayed, the frequency of occurrence, or the percentage of occurrence. Use the same scale for each bar! The graph has a title, labels for each bar, and vertical scale or actual value for the length of each bar
Page 55 Example 4 – Bar GraphFigure 2-11 shows two bar graphs depicting the life expectanciesfor men and women born in the designated year. Let’s analyzethe features of these graphs. The graphs are clustered bar graphs One bar represents the life expectancy for men, and the other represents the life expectancy for women. The height of each bar represents the life expectancy (in years). Figure 2-11(b) is that of a changing scale. The scale between 0 and 65 is compressed. The changing scale amplifies the apparent Life Expectancy difference between life spans for men and Figure 2-11 women, as well as the increase in life spans from those born in 1980 to the projected span of those born in 2010.
Page 56 Pareto Charts A Pareto Chart is a bar graph in which that bar height represents frequency of an event and the bars are ordered from highest to lowest. Example of a Pareto Chart:
Page 57 Circle Graphs A circle graph or pie chart is another way to represent data. Wedges of the circle display proportional parts of the total population that share a common characteristic. Wedges are usually labeled with percentages The total quantity is 100%, represented by the entire circle Example of a Circle Graph:
To Make a Circle Graph1. Find the percentage (relative frequency or fractional part times 100) for each class/category. Do your percents add up to 100%?2. Find the number of degrees for each class/category: Number of Degrees = % • 360˚3. Draw the circle graph. Divide the circle into wedges with the designated number of degrees. Label each piece with its class/category and percentage. Colors are extremely helpful!
Page 58 Time-Series Graphs and Data A time-series graph is a graph that shows data measurements in chronological order. Data are plotted in order of occurrence at regular intervals over a period of time. Example of a Time- Series Graph:
Time-Series Graphs and Data Time-series data consist of measurements of the same variable for the same subject taken at regular intervals over a period of time.
To Make a Time-Series Graph1. Put time on the horizontal scale and the variable being measured on the vertical scale2. Plot the data as points, connect the points with line segments
Page 59How to Decide Which Type of Graph to Use Bar Graphs Quantitative or qualitative data Quantitative Data: measurement itself can be shown Beware of changing scales and jumps Pareto Charts Identify the frequency of events or categories in decreasing order Circle Graphs Display how the total is dispersed in several categories Best if there are 10 or fewer wedges Good for qualitative data (or any data for which percentages make sense) Time-series Graphs Display how data change over time Units of time should be consistent
For All Graphs Provide a title, label the axes, and identify the units of measure. Do not let artwork or skewed perspective cloud the clarity of the information displayed. AP Test: You will be harshly penalized for a lack of titles and labels!