Caffaro & Conn-Caffaro (1998; 2005) define sibling sexual abuse as sexual behavior between siblings for which the victim is not developmentally prepared, which is not transitory, and which does not reflect age-appropriate curiosity. It may or may not involve physical touching, coercion, or force. Bank and Kahn found that most sibling incest fell into one of two categories: "nurturance-oriented incest" and "power-oriented incest". The former is characterized by expressions of affection and love, while the latter is characterized by force and domination.