Presentation on theme: "The Bar Graph or Bar Chart What is it? How to Draw it."— Presentation transcript:
The Bar Graph or Bar Chart What is it? How to Draw it
2 What is a Bar Graph? A bar graph is a graph that displays the frequency or numerical distribution of a categorical variable, showing values for each bar next to each other for easy comparison. Alternate Name: Bar Chart
3 Bar Graph Example In June 2005, the US Dept of Transportation reported the following data by observing 1700 motorcyclists nationwide at randomly selected roadway location: –Proper Helmet 731 –Insufficient Helmet 153 –No Helmet 816 Total1,700
5 x-axis & y-axis Variables On a vertical bar graph, the y-axis variable is normally a quantitative variable. Is it discrete or continuous? On a vertical bar graph, the x-axis variable is normally a categorical variable Categorical Variable
6 Type of Variables on the Previous Motorcycle Bar Graph x-axis? Categorical Variable. Name the categories Proper, Insufficient, None y-axis Discrete Quantitative Variable What are the units? Helmets
7 Making a Bar Graph Look Better What would make this bar graph look better? If we ranked the numbers by either increasing or decreasing value, the appearance would be less jagged, making a Pareto Chart. What is a Pareto Chart? A bar graph in which the bars are ordered according to value, in either increasing or decreasing order. Why Pareto Charts? Graph is named for Vilfredo Pareto, an Italian mathematician & economist. 1848-1923.
14 Bar Graphs: VERY FLEXIBLE FORMAT Advantage over Pie Charts Bar Graphs are easier to make & to read than pie charts. How are they similar to Pie Charts? Both pie charts & bar graphs can display the distribution of a categorical variable How are they different from Pie Charts? A bar graph can also compare any set of quantities measured in the same units.
25 Bar Graph Characteristics 1.Data can be quantitative or categorical 2.Bars can be vertical or horizontal 3.The x-axis represents the category displayed 4.The y-axis represents the quantitative values of the variable being displayed 5.Bars are of uniform width and uniformly spaced
26 Bar Graph Characteristics 6.A consistent measurement scale is used for each vertical bar 7.Height of bars represent the values of the variable displayed, the frequency of occurrence or percentage of occurrence 8.The graph is well-annotated with title, labels for each bar, vertical scale, horizontal categories, source
27 Changing Scale – The Squiggle What is a squiggle? At least a 2-angle line on a bar graph axis that abbreviates a scale. When do you use a squiggle? Use a squiggle on the changed axis whenever you change scale in a bar graph. Horizontal SquiggleVertical Squiggle or
36 “Would The Bar Graph Make a Good Pie Chart?” Only when Bar Graphs represent parts of a whole, can it be made into a Pie Chart. If the answer is NO, you could write: –No, because these values are comparative data only. –No, because these values DO NOT represent parts of the whole. If the answer is YES, you could write: –Yes, because these values represent parts of the whole.
37 Bar Graph & Pie Chart Relationship Summary Every Pie Chart COULD be made into a Bar Graph BUT NOT all Bar Graphs CAN be made into Pie Charts Pie Chart Bar Graph Bar Graph Pie Chart
46 Deciding Which Graph is Better The Chicago Tribune polled 380 randomly selected Chicago residents from August 27 to 31, 2009 on the subject of the potential Chicago Olympics of 2016. The question asked was, “Do you favor or oppose Chicago hosting the 2016 Olympic games?” The results of the poll were: Supply the remainder of the data labels
47 Could the Pie Chart Become a Bar Graph? The answer is obviously yes, But the question remains, Which Graph looks better? Which Graph is better for display purposes? This is a matter of opinion Supply the remainder of the data labels
48 Examining a Bar Chart for Meaning What’s the question? What’s the title? What’s the population? What’s the sample? How many variables? What are they? What’s the conclusion? Good pie chart? Is this a Pareto chart?
62 Steps in Bar Chart Construction 1.Use a straight edge on a piece of graph paper 2.Make a first-quadrant x-y axis, unless some of your data is negative 3.Examine the data and determine the maximum value of the quantitative data. Your y-scale must be at least this high
63 Steps in Bar Chart Construction 4.Choose an appropriate scale for the y- axis. 5.Mark scale ticks consistently & label them, until you reach a mark greater than the highest value of data. 6.Mark of the bar width of each piece of categorical data you will be using on the x-axis.
64 Steps in Bar Chart Construction 7.Make sure you place a space between each of the data bars. 8.Plot each data point by drawing a bar of the correct width & height for each. 9.Label the top of each bar with a value. 10.Label both x- and y-axes with a title 11.Title the graph 12.Label the source of the data.
72 Hints: Complete the Vocabulary Then do the front page Place your HW in the HW box Quiz #103 Bar Charts You need: Pencil, Eraser Calculator Graph Paper (for 2 graphs: one sheet okay) No bags on desk Clear all lists in Calculator