Also see Why controlled crying/comforting is harmful and its alternatives in Sleep
For crying out loud - pick up your baby by Queensland University of Technology
"It is also important for parents to have the confidence to trust their instincts when it comes to caring for their baby". However "a joint study with Queensland University of Technology and the Riverton Early Parenting Centre has found many parents of infants up to 12 weeks, were uncertain about how best to settle their crying baby and whether or not it was 'right' to pick them up"(Source).