The Bar Graph or Bar Chart What is it? How to Draw it What is a Bar Graph?

 Date 30.04.2018 Size 14.68 Kb. #42365

The Bar Graph or Bar Chart

• What is it? How to Draw it

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

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
• Total 1,700

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

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

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.

• Non Pareto
• Version of
• Sales

Bar Graphs: VERY FLEXIBLE FORMAT

• 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.

Psychic Phenomena

• Pareto Chart of Psychic Phenomena

Bar Graph Characteristics

• Data can be quantitative or categorical
• Bars can be vertical or horizontal
• The x-axis represents the category displayed
• The y-axis represents the quantitative values of the variable being displayed
• Bars are of uniform width and uniformly spaced

Bar Graph Characteristics

• A consistent measurement scale is used for each vertical bar
• Height of bars represent the values of the variable displayed, the frequency of occurrence or percentage of occurrence
• The graph is well-annotated with title, labels for each bar, vertical scale, horizontal categories, source

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 Squiggle Vertical Squiggle
 or

“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.

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

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:

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

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?

Steps in Bar Chart Construction

• Use a straight edge on a piece of graph paper
• Make a first-quadrant x-y axis, unless some of your data is negative
• Examine the data and determine the maximum value of the quantitative data. Your y-scale must be at least this high

Steps in Bar Chart Construction

• Choose an appropriate scale for the y-axis.
• Mark scale ticks consistently & label them, until you reach a mark greater than the highest value of data.
• Mark of the bar width of each piece of categorical data you will be using on the x-axis.

Steps in Bar Chart Construction

• Make sure you place a space between each of the data bars.
• Plot each data point by drawing a bar of the correct width & height for each.
• Label the top of each bar with a value.
• Label both x- and y-axes with a title
• Title the graph
• Label the source of the data.

What Comes After High School?

• Pareto Chart of “Path After Graduation”

Mountains to Climb

• 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