WASHINGTON POST - Feb 14 - According to app analytics website AppAnnie, Tinder has been the most downloaded lifestyle app in America for two years. Tinder's approach to romance is straightforward, yet brutally effective. Matches are made using sparse criteria: Looks, availability and location. Tinder's interface is perfectly constructed to encourage rapid swiping. Since users don't know which swipe will bring the "reward" of a match, Tinder uses a variable ratio reward schedule, which means that potential matches will be randomly dispersed. It's the same reward system used in slot machines. In a study on the brains of drug addicts, researchers found that the expectation of the drug caused more release of the feel-good neurotransmitter dopamine than the actual drug itself. Similarly, for those who may be expecting the next swipe on Tinder to lead to reward, serial swiping can start to look and feel a lot like addiction. So in 2015 Tinder began to limit the amount of daily right swipes to 100 for users who don't buy into their premium service.