Increased carrying reduces infant crying:
a randomized controlled trial.

Pediatrics 1986 May;77(5):641-8.

“..We hypothesized that this \"normal\" crying could be reduced by supplemental carrying, that is, increased carrying throughout the day in addition to that which occurs during feeding and in response to crying.”
 
“In a randomized controlled trial, 99 mother-infant pairs were assigned to an increased carrying or control group.”
 
“At the time of peak crying, infants who received supplemental carrying cried and fussed 43% less overall, and 51% less during the evening hours (4 PM to midnight). ”
 
“We conclude that supplemental carrying modifies \"normal\" crying by reducing the duration and altering the typical pattern of crying and fussing in the first 3 months of life. The relative lack of carrying in our society may predispose to crying and colic in normal infants.”
 
See Full Abstract Here

Three hours of carrying a day reduced the amount of crying in a four-week-old infant by forty-five percent reported a study published in Pediatrics. 

“In healthy infants, crying behavior is reduced significantly by \"supplemental\" carrying; that is, increased carrying throughout the day in addition to that which occurs during feeding and in response to crying.”
 

See Full Abstract Here

 For more information on slings and babywearing in relation to colic in infants, please see The Continuum Concept.