The Power of Positive Thinking of followers testified that Peale’s message changed their lives for the better and represented the best combination of faith and pragmatism.” This is evidenced by the popularity of Peale's book, which sold more than 5 million copies worldwide and was eventually translated into over 40 languages. In addition, Peale was close friends with American presidents Eisenhower and Nixon, both of which highly regarded his positive thinking teachings. Countless others accredited "The Power of Positive Thinking" for their success in overcoming obstacles including George Foster, of the Cincinnati Reds, Rev. Robert Schuller, founder and pastor of the Crystal Cathedral in Garden
Positive psychology for someone of low skills results in a state of anxiety; insufficient challenge for someone highly skilled results in boredom. Research in positive psychology, well-being, eudaimonia and happiness, and the theories of Diener, Ryff, Keyes and Seligman cover a broad range of topics including "the biological, personal, relational, institutional, cultural, and global dimensions of life". A meta-analysis on 49 studies in 2009 showed that Positive Psychology Interventions (PPI) produced improvements in well-being and lower depression levels, the PPIs studied included writing gratitude letters, learning optimistic thinking, replaying positive life experiences and socializing with others. In a later meta-analysis of 39