The research, carried out by academics at Columbia University and the University of Pittsburgh, reveals that catching up with friends and socializing online can have a positive effect on self-esteem and well-being.
Given that many readers of self-help books that encourage positive self-statements are likely to suffer from low self-esteem, they may be worse than useless.
Dr Wood suggests that positive self-statements cause negative moods in people with low self-esteem because they conflict with those people's views of themselves.