Overall, studies indicate that 15 to 20 percent of one to three year olds continue to have nightwakings. According to an expert, “Inappropriate sleep associations are the primary cause of frequent nightwakings. Sleep associations are those conditions that are habitually present at the time of sleep onset and in the presence of which the infant or child has learned to fall asleep. These same conditions are then required in order for the infant or child to fall back to sleep following periodic normal nighttime arousals.”