The Power of Positive Thinking believe and live successfully.” Peale's work came under criticism from various mental health experts, theologians, and academics. One general criticism against Peale's book was the lack of verified sources. "The Power of Positive Thinking" includes many personal anecdotes that the reader has no way of validating. The book includes stories about “a business executive”, “a man, an alcoholic”, “a famous trapeze artist”, “a friend of [Peale’s], a midwestern businessman”, and other unnamed individuals which cannot be verified from the information Peale presents with each anecdote. R. C. Murphy, a prominent psychiatrist based out of Tacoma, Washington, addresses another criticism of
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