Describing Data Visually 3 Describing Data Visually Chapter Visual Description Dot Plots Frequency Distributions and Histograms Line Charts Bar Charts Scatter Plots Tables Pie Charts Descriptive Graphs McGraw-Hill/Irwin Copyright © 2010 by The McGraw-Hill Companies, Inc. All rights reserved. 1

Visual Description Methods of organizing, exploring and summarizing data include: - Visual (charts and graphs) provides insight into characteristics of a data set without using mathematics. - Numerical (statistics or tables) provides insight into characteristics of a data set using mathematics. 2

Dot Plots Comparing Groups A stacked dot plot compares two or more groups using a common X-axis scale. 3

Frequency Distributions and Histograms A frequency distribution is a table formed by classifying n data values into k classes (bins). 4

Frequency Distributions and Histograms A histogram is a graphical representation of a frequency distribution. Y-axis shows frequency within each bin. A histogram is a bar chart. X-axis ticks shows end points of each bin. 5

Frequency Distributions and Histograms 6

Frequency Polygon and Ogive 7

Line Charts Simple Line Charts Two-scale line chart – used to compare variables that differ in magnitude or are measured in different units. A line graph usually has no vertical grid lines. Horizontal lines can be added to make it easier to establish the y value. 8

Line Charts Log Scales Log scale is only suited for positive data values. Reveals whether the quantity is growing at an increasing percent (concave upward), constant percent (straight line), or declining percent (concave downward) 9

Bar Charts Plain Bar Charts Most common way to display attribute data. - Bars represent categories or attributes. - Lengths of bars represent frequencies. Vertical Bar Chart Horizontal Bar Chart 10

Bar Charts Pareto Charts Special type of bar chart used in quality management to display the frequency of defects or errors of different types. Categories are displayed in descending order of frequency. Focus on significant few (i.e., few categories that account for most defects or errors). 11

Scatter Plots Scatter plots can convey patterns in data pairs that would not be apparent from a table. 12

Tables Tables are the simplest form of data display. A compound table is a table that contains time series data down the columns and variables across the rows. 13

Pie Charts Pie Chart Options Exploded and 3-D pie charts add strong visual impact but slices are hard to assess. Exploded Pie Chart Exploded 3-D Pie Chart

Effective EXCEL Charts Effective visual displays help you get your point across and persuade others to listen to your point of view. Powerful graphics stands out in reports which helps in better decision making. Excel is widely used primarily because of its excellent graphics capabilities. Excel offers a vast array of charts. You need to experiment in creating graphs with Excel to get familiar with its features and how you can create effective graphs.

Deceptive Graphs Error 1: Nonzero Origin Error 2: Elastic Graph Proportions Error 3: Dramatic Title Error 4: Distracting Pictures Error 5: Authority Figures Error 6: 3-D and Rotated Graphs Error 7: Missing Axis Demarcations Error 8: Missing Measurement Units or Definitions Error 9: Vague Source Error 10: Complex Graphs Error 11: Gratuitous Effects Error 12: Estimated Data Error 13: Area Trick 16