Our SAGs: Design Aspects and Improvements - Semantic Acquisition Games: Harnessing Manpower for Creating Semantics - page 130

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For explicit tag rule-out, the player gains minor number of points (same as with
tag buying). This gain is always constant, regardless of how many tags the player
rules out. As we have described before, the main motivation for the player in this
case, is the “investment into future”.

Note that the scale of the point gains is not so important (for instance, the bet values
100 and 200 would work just as well as 500 and 1,000), the important is to keep the
proportions between major and minor point changes so the minor game actions (tag
buying, tag rule-outs) remain interesting for the player but do not overrun the main
scoring “function” (the betting).
If the player successfully finishes a game, his remaining score points are saved
and added to his total score, which is kept over time. Total score serves as a means
for sorting the players to a ladder. However, as recommended by Luis von Ahn [ 6 ],
the motivational effects of the ladders and scoring systems are better, if they are
complemented with the “experience” and “player level” system, which originally
emerged in the classical role-playing games, where player develops his personal
avatar.
In an experience/level system, which we also employed in the CityLights, the
score has a form of experience points, which indicate how much effort the player
had invested in the game. Furthermore, each player has also a level , which indicates
that he had reached a certain milestones. In a common case, the player reaches a
next level after he gains a certain number of experience points. The level is then the
primary mean of comparing of the players and has several advantages:

1. The milestones represent a longer term challenges (in comparison to the finishing
of the game) and motivate players to play more.
2. The comparison of players more understandable with small numbers of level
values than large numbers of experience values.
3. New players with low levels feel more confident to reach the high ranking players.
This is because the relation between the experience and level increase is loga-
rithmic (with the linear experience increase, the level rises on the logarithmic
basis) and therefore, even the players with extremely high experience seem to be
relatively close to the new players in the ladder, which motivates the new players
for further playing.
4. The minor differences in the experience counts nivelize groups of players to one
level and by this further encourages their competition as every player wants to
distinguish himself by higher level than others have.

The experience and level system of the CityLights follows the principles described
above. The player engages it through multiple ladders and level gauge in the main
menu of the game application (see Fig. 8.3 ). The level gauge (top-right corner) indi-
cates, how much experience he needs for reaching the next level. The three ladders
(overall, monthly and weekly) propose other short and long term challenges for the
player (“be the first this month”).