When is it wrong and/or inappropriate to use a slash mark?
Do not use a slash (also called a virgule, solidus, or shill)
when a phrase would be clearer
Each child handed the ball to her mother or guardian.
not
Each child handed the ball to her mother/guardian.
test–retest reliability
not
test/retest reliability
nmol • hr-1 • mg -1
not
nmol/hr/mg
(adapted from the sixth edition of the APA Publication Manual, © 2010)