Error bars are smaller vertical lines extending upward and downward from the top of each main bar or point in a graph. They visually represent the variability within each group or condition, typically depicting one standard error or one standard deviation in each direction.

Error Bars

A bar graph can be used to visualize differences in mean scores across categorical conditions. For example, a bar graph can display the mean clinician rating of severity for three different experimental groups: an Education condition, an Exposure condition, and a Control condition. The categorical conditions are plotted on the horizontal axis, and the quantitative severity ratings are plotted on the vertical axis. The data shows that the Control condition resulted in the highest severity rating ($$5.56$$), compared to the Education ($$4.83$$) and Exposure ($$3.47$$) conditions.

Example of a Bar Graph: Clinician Rating of Severity

An APA-style bar graph can effectively present the results of an experiment by comparing mean scores across categorical conditions, such as in the research by Ollendick and colleagues. In such graphs, error bars are typically added to the top of each main bar, extending one standard error upward and downward. This visual addition allows readers to observe the variability within each group and visually estimate whether the differences between the group means are statistically significant.

Example of an APA-Style Bar Graph

According to standard research conventions, what type of independent variable is typically plotted on the x-axis when using a bar graph to present and compare mean scores?

A researcher wants to visually compare the mean anxiety scores among three distinct treatment groups. According to standard research conventions, a bar graph would be an appropriate way to present this data.

Bar graphs are commonly used in research to present and compare the mean scores for two or more groups or conditions. Following conventions, researchers typically use a bar graph when the independent variable plotted on the $$x$$-axis is categorical.

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The APA Publication Manual establishes technical guidelines for the layout of graphs. Generally, scatterplots, bar graphs, and line graphs should be constructed to be slightly wider than they are tall. The independent variable must be plotted on the $$x$$-axis, and the dependent variable on the $$y$$-axis. Furthermore, numerical values must increase from left to right on the $$x$$-axis and from bottom to top on the $$y$$-axis, with both axes strictly beginning at the value of zero.

Layout of APA Style Graphs

https://kpu.pressbooks.pub/psychmethods4e/

KPU Research Methods in Psychology - 4th American Edition

APA Style Bar Graphs

Line graphs are utilized in research reporting when the independent variable on the $$x$$-axis is measured continuously, such as time, or to display correlations between quantitative variables when the independent variable is organized into a small number of distinct levels. Each plotted point on a line graph represents the mean score on the dependent variable for participants at a single level of the independent variable, and these points often include error bars to visualize standard error.

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