“…With concern to the number of players involved, only six studies [ 44 , 54 , 56 , 68 , 75 , 76 ] consider developing the game also as a multiplayer platform, while the other studies refined the game only for single players. However, some studies [ 45 , 47 , 54 , 56 , 57 , 60 , 63 , 64 , 68 , 77 ] also included one or more non-player characters (NPCs), i.e., those characters in a game which are not controlled by the player but by the computer.…”