Interpreting Error Bars

What is the primary purpose of error bars in a graph?

• To color code the data points

• To separate different groups visually

• To indicate the level of uncertainty in data

• To make the graph look more complex

What statistical value is typically used to determine if groups differ significantly?

• Mean value

• Standard deviation

• Median value

• P-value

If error bars do not cross, what can be inferred about the groups?

• Groups are likely from the same sample

• Error bars are incorrectly placed

• There is no significant difference between groups

• There is likely a significant difference between groups

Which type of error bar suggests a significant difference if they do not cross?

• Range bars

• Confidence interval bars

• Variance bars

• Standard deviation bars

In AP Biology we use +/- 2 Standard Error of the Mean (2SEM). These bars are essentially like stating Confidence Intervals (as CI data is generated using SEM). So, if error bars from 2SEM overlap, we must conclude:

• The data is not statistically different.

• The data is statistically different.