Factors having a negative effect on compliance included the older age of the child and the long duration of the study. In describing attrition rates in 40 different pediatric cognitive therapy trials for chronic illnesses including asthma, diabetes, sickle cell anemia, cystic fibrosis, Karlson and Rapoff (2009) noted that the mean attrition rate was 20% (range 0-54%) for initial follow—up and 32% (range O-59%) for extended follow—up. They recommended strategies to improve retention including tailoring recruitment to the study population, providing personalized feedback, maintaining consistent study procedures, providing incentives, and using intensive tracking measures.