to separate two independent clauses that are not joined by a conjunction
For example:
The participants in the first study were paid; those in the second were unpaid.
to separate elements in a series that already contain commas
For example:
The color order was red, yellow, blue; blue, yellow, red; or yellow, red, blue.
(Davis & Hueter, 1994; Pettigrew, 1993)
main effects of age, F(1, 76) = 7.86, p <.01, d = .09 (MSE = .019); condition, F(1,76) = 4.11, p = .05, d = .06; and the Age x Condition interaction, F(1, 76) = 4.96, p = .03, d = .07