Logo IMG   Conscientious Subjects  To the Editors:  I enjoyed
the article “Lifelong Impact of Early Self-Control”
(September–October) by Terrie Moffitt, Richie Poulton, and
Avshalom Caspi, reporting on an interesting study that has
significant social policy implications.  They presented strong
evidence that people who show good self-control capabilities at
three years of age tend to be more successful in various ways
later in life, and then discussed at length how self-control
might be enhanced in order to improve people’s lives. On an
intuitive level, I find it credible that a person’s self-control
capability would be instrumental—causally related—to success in
life. However, some of the analysis presented seems to suggest
that self-control, while indicative of success, may not be
instrumental.  The analysis shows that higher levels of self-
control at age three are strongly correlated with success in
life. But self-control levels at older ages are only weakly
correlated with self-control at age three. This h