The Power of Positive Thinking Happiness," published in 1950, and "Inspiring Messages for Daily Living", published in 1955. "The Power of Positive Thinking" appeared at a time when Christian church attendance was drastically increasing, national views of spirituality, individuality, and religion were shifting, and the Cold War was a growing concern for many Americans. These factors, as well as Peale's growing popularity as a motivational public figure and the book's clear prose, propelled "The Power of Positive Thinking" into a self-help book still popular today. Peale begins by stating ten rules for “overcoming inadequacy attitudes and learning to practice faith”. The rules include the following:
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