Use a serial comma (also called an Oxford comma, Harvard comma, or series comma) between elements in a series of three or more items.
Factors of personality include extraversion, conscientiousness, openness to experience, agreeableness, and neuroticism.
Commas are covered in Section 6.3 of the APA Publication Manual, Seventh Edition
This guidance is the same as in the 6th edition.
If one or more items in the series already contain a comma, use semicolons between the items instead of commas.
Subjective well-being is characterized by the presence of positive affect, such as whether people feel happy and peaceful; the absence of negative affect, such as whether people feel angry or bored; and a high level of life satisfaction.