by Timothy McAdoo
Today I want to zero in on a special topic. This is not just an empty set of words: Let’s de-cipher another APA Style point!
The zero before a decimal point is known as a leading zero. Have you noticed that sometimes this zero is used in decimal values and sometimes it is not?
APA Style has a very simple guideline for leading zeros:
- If a value has the potential to exceed 1.0, use the leading zero.
- If a value can never exceed 1.0, do not use the leading zero.
Thus, because most units of measure have the potential to exceed 1.0, the leading zero is frequently needed. A value over 1.0 does not need to actually appear in the text. Here are just a few examples:
|…was 0.75 in. tall by 0.95 in. wide.
Participants viewed, on average, less than 0.65 hr of the footage.
…had means of 1.01, 2.21, and 0.95, respectively.
…had 95% CIs [0.62, 1.12], [-2.44, 4.30], and [-3.19, -2.39], respectively.
There are some values that by definition can never exceed 1.0. The omission of the leading zero is a visual indicator of this restricted range. The most common cases are p values and correlations:
|…was significant (p < .01).
…was significant (p = .001).
…was shown to be highly correlated (r = .71).
A consistent presentation of statistical values, both within a paper and across published articles, provides a visual symmetry that can help readers focus on content over form.
I hope this zippy post has helped nullify any confusion. If you’re still drawing a blank, you can also find this guideline and additional examples on page 113 of the Publication Manual of the American Psychological Association (6th ed.).