When did TV shows start showing previews of next weeks episodes?

by kamson Tue 15 Jun 2010, 10:06

Just wanting to know when TV shows started showing clips of Next Weeks Episode at the end of Today's episode? What I mean is Next week on Criminal Minds people are missing who is it.

Don't remember seeing this much if at all in the 1970's, 1980's, or most of the 1990's. Have TV shows always done this, or is just something they have recently started and if so what year did they start doing this? Is this to get you to not make other arrangements so you will watch the show next week?