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June 17, 2010

Formatting Statistics: Using Brackets

Timothy McAdoo by Timothy McAdoo

In the previous post, we discussed how to use parentheses and commas with statistics.

Today, we highlight an exception to this guideline. There are two cases when brackets are the preferred choice in APA Style.

First, when parenthetical text also includes a statistic, brackets should be used.

(See Figure 3 for the results from the control group [n = 8]; compare with results from the Pink Floyd listening group [n = 23] and the Beatles listening group [n = 41].)

Second, for clarity, APA Style recommends that confidence intervals be reported with brackets around the upper and lower limits (as outlined on page 117):

95% CI [5.62, 8.31]

In the context of a sentence this might look like the following:

Participants who heard one Dresden Dolls song on repeat for 180 min reported no less anxiety than those who heard one Mozart movement on repeat for 180 min, R2 = .22, F(1, 32) = 7.33, p = .003, 95% CI [0.11, 1.23]. Our hypothesis that the genre difference would influence anxiety levels was rejected.

Also, as noted in the Publication Manual of the American Psychological Association (6th ed.) on page 117, every report of a confidence interval must clearly state the level of confidence. Multiple confidence intervals would appear as follows. Notice the plural version of the CI abbreviation:

... 95% CIs [5.62, 8.31], [-2.43, 4.31], and [-4.29, -3.11], respectively.

I hope these examples are helpful.  What other questions about formatting statistics do you have? Let us know in the comments.

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