Several studies have argued that an isolated incident of verbal aggression, dominant conduct or jealous behaviors does not constitute the term "psychological abuse." Rather, it is defined by a pattern of such behaviors, unlike physical and sexual maltreatment where only one incident is necessary to label it as abuse. Tomison and Tucci write, "emotional abuse is characterised by a climate or pattern of behavior(s) occurring over time [...] Thus, 'sustained' and 'repetitive' are the crucial components of any definition of emotional abuse." Andrew Vachss, an author, attorney and former sex crimes investigator, defines emotional abuse as "the systematic diminishment of another. It may be intentional or subconscious (or both), but it is always a course of conduct, not a single event."