# Which type of statistical information will need Error Bar charts for presentation?

When presenting statistical information using bar charts, when will you need to use Error Bar charts?

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Adding error bars to a bar graph is a choice you make as a presenter to communicate more information to your audience. They are useful because they communicate visually how certain you can be, based on your data, of the specific values you are presenting.

In some cases, there is no uncertainty. Imagine you are graphing the number of students in each grade in a school district. These numbers are known so presenting the exact values without error bars makes sense.

If however you are graphing the height of students by gender and you only had time to measure students in one class, you are making statistical inferences about the larger population. In this case, error bars are helpful to communicate the range of likely true values. If the 15 boys in the class you measured averaged 48 inches you could include error bars to show that you are 95% sure that the average of all boys in the district is between say, 46 and 50.

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