Bar Charts

Qualitative Variables and Bar Charts

  • Bar charts are effective for displaying the frequencies of different categories.

    • Example: A bar chart illustrating purchasers of iMac computers categorized as:

    • Previous Macintosh users: Just over 350

    • Previous Windows users: About 60

    • New computer purchasers: About 75

Quantitative Information and Percent Changes

  • Bar charts can also present quantitative information, such as percent changes.

    • Example: Bar chart of percent increases in major stock indexes from 05/24/2000 to 05/24/2001:

    • S&P 500 and NASDAQ showed negative increases, indicating a decrease in value.

    • The y-axis represents percentage change rather than frequency.

Consumer Price Index (CPI) Over Time

  • Another example of a bar chart presenting data over time:

    • Displays percent increases in the Consumer Price Index (CPI) across four three-month periods.

    • CPI Definition: Represents how much typical consumer items cost.

    • Notable findings:

    • Greatest increase occurred in January 2001.

    • Smallest increase observed in April.

Bar Charts for Experimental Conditions

  • Bar charts are commonly utilized to compare the means of different experimental conditions.

    • Example: Mean time taken to move a computer mouse to targets of varying sizes:

    • Small targets: Mean time = over 700 milliseconds.

    • Large targets: Mean time = a little over 500 milliseconds.

    • Insight: More time is required for small targets compared to large targets.

Limitations of Bar Charts

  • Although it is a common practice to use bar charts for displaying means, it is not recommended for this purpose.

Box Plots as a Better Alternative

  • Box plots should be used instead of bar charts because:

    • They provide more information regarding the distribution of data.

    • They require less space than bar charts.

    • Example: A box plot of mouse movement data reveals distribution characteristics that a bar chart cannot convey adequately.

  • Conclusion: Using box plots is a better practice for displaying statistics such as means, as they can convey richer data insights in the same amount of space compared to bar charts.