tokens: Least preferred methods included online discussions / chatrooms ( mean 1 . 52 , SD 1 . 04 ) , internet videos ( live : mean 1 . 70 , SD 1 . 10 , or static : mean 1 . 87 , SD 1 . 14 ) , video cassettes ( mean 2 . 30 , SD 1 . 55 ) , trial and error learning ( mean 2 . 32 , SD 1 . 28 ) , and written manuals ( mean 2 . 92 , SD 1 . 44 ) .