This is a local cache copy of the article published by Dr. Jeffrey Kahn from Illinois State University.

http://my.ilstu.edu/~jhkahn/apastats.html

Reporting Statistics in APA Style

Dr. Jeffrey Kahn, Illinois State University

The following examples illustrate how to report statistics in the text of a research report. You will note that significance levels in journal articles–especially in tables–are often reported as either "p > .05," "p < .05," "p < .01," or "p < .001." APA style dictates reporting the exact p value within the text of a manuscript (unless the p value is less than .001).

Please pay attention to issues of italics and spacing. APA style is very precise about these. Also, with the exception of some p values, most statistics should be rounded to two decimal places.


Mean and Standard Deviation are most clearly presented in parentheses:

The sample as a whole was relatively young (M = 19.22, SD = 3.45).

The average age of students was 19.22 years (SD = 3.45).

Percentages are also most clearly displayed in parentheses with no decimal places:

Nearly half (49%) of the sample was married.

Chi-Square statistics are reported with degrees of freedom and sample size in parentheses, the Pearson chi-square value (rounded to two decimal places), and the significance level:

The percentage of participants that were married did not differ by gender, c2(1, N = 90) = 0.89, p = .35.

T Tests are reported like chi-squares, but only the degrees of freedom are in parentheses. Following that, report the t statistic (rounded to two decimal places) and the significance level.

There was a significant effect for gender, t(54) = 5.43, p < .001, with men receiving higher scores than women.

ANOVAs (both one-way and two-way) are reported like the t test, but there are two degrees-of-freedom numbers to report. First report the between-groups degrees of freedom, then report the within-groups degrees of freedom (separated by a comma). After that report the F statistic (rounded off to two decimal places) and the significance level.

There was a significant main effect for treatment, F(1, 145) = 5.43, p = .02, and a significant interaction, F(2, 145) = 3.24, p = .04.

Note from Shen: since ANOVA only report if there is a significant effect without revealing the details of the effect, it is often useful to further explain the effect with additional details.

Here is an example taken from statistics help for students.com.

Post hoc comparisons using the Tukey HSD test (or you can replace this with t Test or t Test with Bonferroni correction) indicated that the mean score for the sugar condition (M = 4.20, SD = 1.30) was significantly different than the no sugar condition (M = 2.20, SD = 0.84). However, the a little sugar condition  (M = 3.60, SD = 0.89) did not significantly differ from the sugar and no sugar conditions.

You also want to report your results in words that people can understand, as follows.

Taken together, these results suggest that high levels of sugar really do have an effect on memory for words. Specifically, our results suggest that when humans consume high levels of sugar, they remember more words. However, it should be noted that sugar level must be high in order to see an effect. Medium sugar levels do not appear to significantly increase word memory.

 

Correlations are reported with the degrees of freedom (which is N-2) in parentheses and the significance level:

The two variables were strongly correlated, r(55) = .49, p < .01.

Regression results are often best presented in a table. APA doesn’t say much about how to report regression results in the text, but if you would like to report the regression in the text of your Results section, you should at least present the unstandardized or standardized slope (beta), whichever is more interpretable given the data, along with the t-test and the corresponding significance level. (Degrees of freedom for the t-test is N-k-1 where k equals the number of predictor variables.) It is also customary to report the percentage of variance explained along with the corresponding F test.

Social support significantly predicted depression scores, b = -.34, t(225) = 6.53, p < .001. Social support also explained a significant proportion of variance in depression scores, R2 = .12, F(1, 225) = 42.64, p < .001.

Tables are useful if you find that a paragraph has almost as many numbers as words. If you do use a table, do not also report the same information in the text. It’s either one or the other.


Based on: American Psychological Association. (2010). Publication manual of the American Psychological Association (6th ed.). Washington, DC: Author.

Written by Shengdong Zhao

Shen is an Associate Professor in the Computer Science Department, National University of Singapore (NUS). He is the founding director of the NUS-HCI Lab, specializing in research and innovation in the area of human computer interaction.