Final answer:
Kelly is at a higher risk of developing depression and anxiety disorders by the time she is 21 years old.
Step-by-step explanation:
The researcher noted in your text suggests that Kelly, who was described as being 'under control' at 3 years old, is at a higher risk of developing depression and anxiety disorders by the time she reaches 21 years old (Moffitt et al., 2007).
Research has shown that certain risk factors such as childhood environment, temperament, and genetic predisposition can contribute to the development of these mental health conditions (Joyce et al., 2003). In addition, a study by Friedman and Booth-Kewley (1987) found that personality traits like depression, anger/hostility, and anxiety are associated with a higher risk of developing chronic health problems and mortality.