Final answer:
The quality measured in Mischel's marshmallow study was self-regulation and delay of gratification, predicting various successful outcomes later in life.
Step-by-step explanation:
The study mentioned in the Van Epp book refers to Walter Mischel's marshmallow test, which measured self-regulation and delay of gratification in young children. The study found that children who were able to wait longer for a bigger reward (delay gratification) demonstrated greater self-regulation and were more successful in various outcomes later in life, such as higher SAT scores, better peer relationships, and less likelihood of substance abuse issues. Conversely, those with poorer self-control tended to have more academic and behavioral problems. Subsequent research has indicated that these associations, while present, may also be influenced by situational factors such as cognitive capacity, family background, and home environment.