What is meant by the term "random combination" relating to advertising/marketing? Thanks?

Question

media research term. refers to different mediums?

Answer 1

It would help to provide context.  My guess is that you are referring to a formula to determine the reach of advertising on two different media.  I'm not certain whether that's what you are referring to because the term is more commonly "random duplication".  The assumption is that duplication between the media is random, that users of one medium are neither more nor less likely to be users of the other.  If you assume random duplication, and you calculate that your print advertising will reach 30% of your population and TV will reach 50%, you calculate that the duplication is 30% of 50% = 15% and your total reach is than 30% + 50% - 15% = 65%.