Probability and Statistics > Reporting Statistics APA Style
APA style can be finicky. Trying to remember the very particular rules for spacing, italics and other formatting rules can be overwhelming if you’re also writing a fairly technical paper. My best advice is to write your paper and then edit it for grammar. Don’t worry about reporting statistics APA style until your paper is almost ready to submit for publication. Then go through your paper and make a second edit for statistical notation based on this list.
1. General tips for Reporting Statistics APA Style
- Use readable spacing, placing a space after commas, variables and mathematical symbols. For example:
- Correct: r(55) = .49, p < .001
- Incorrect: r(55)=.49,p<.001.
APA suggests using two spaces after periods to aid readability, but this is not required.
- Don’t state formulas for common statistics (e.g. variance, z-score). Similarly, don’t use references for statistics unless they are uncommon or the focus of your study.
- Round decimals to two places, with the exception of p-values (see p-values in the next section).
If the decimal is less than one:
- Place a zero before the decimal point if the statistic can be greater than one (e.g. 0.26 lb).
- If number cannot be greater than one, leave out the decimal point (e.g. p = .015).
- All symbols should be italicized: t, F, z. Exceptions:
- Use an uppercase N for number in the total sample (N = 45) and a lowercase n for a fraction of the sample (n = 20).
- Place percentages in parentheses. For example: “Almost a quarter of the sample (25.5%) was already infected with the virus.”
- If you use a table to report results, don’t duplicate the information in the text.
2. Reporting Specific Statistics in APA Style
Confidence intervals: For CIs, use brackets: 95% CIs [2.47, 2.99], [-5.1, 1.56], and [-3.43, 2.89]. If you are reporting a list of statistics within parentheses, you do not need to use brackets within the parentheses. For example (SD = 1.5, CI = -5, 5)
Use parentheses to enclose degrees of freedom. For example, t(10) = 2.16.
P-values: report the p-value exactly, unless it is less than .001. If less than that amount, the convention is to report it as: p < .001.
3. Hypothesis Tests in APA Style
At the beginning of the results section, restated your hypothesis and then state if your results supported it. This should be followed by the data and statistics to support or reject the null hypothesis.
One-Way/Two-Way ANOVA: State the between-groups degrees of freedom, then state the within-groups degrees of freedom, followed by the F statistic and main effect was significant, F(1, 149) = 2.12, p = .02.”
Chi-Square test of Independence: Report degrees of freedom and sample size in parentheses, then the chi-square value, followed by the significance level. For example:
“Animal response to the stimuli did not differ by species, Χ2(1, N = 75) = 0.89, p = .25.”
T Tests: Report the t-value and significance level as follows: t(54) = 5.43,
p < .001. What you put in the wording will differ slightly depending on if you have a one sample t-test, or a t-test for groups. Examples:
- One sample: “Younger teens woke up earlier (M = 7:30, SD = .45) than teens in general. t(33) = 2.10, p = 0.31″
- Dependent/Independent samples: “Younger teens indicated a significant preference for video games (M = 7.45, SD = 2.51) than books (M = 4.22, SD = 2.23), t(15) = 4.00, p < .001.”
Report correlations with degrees of freedom (N-2), followed by the significance level. For example: “The two sets of exam results are strongly correlated, r(55) = .49, p < .001.”
Publication Manual of the American Psychological Association, (6th ed., 2nd printing).
Milan, JE, White, AA. free R Tutorial by Datacamp is a great way to get started. If you're are somewhat comfortable with R and are interested in going deeper into Statistics, try this Statistics with R track.