The invention relates to simple yet effective methods, referred to herein as Dynamic Intermittent Reward or Reinforcement (DIR), and systems, to increase the frequency of a desired behavior in a user, and optimize cost-effectiveness of a reward system. A principal benefit of the new methods is the ability to provide tailored intermittent rewards for one or more users over time. The invention further relates to other methods, referred to herein as Tabular Intermittent Reward or Reinforcement (TIR), and systems, to administer intermittent rewards without an element of chance.