Psychiatrist: While the first appearance of a phobia is usually preceded by a traumatizing event, not everyone who is traumatized by an event develops a phobia. Furthermore, many people with phobias have never been traumatized. These two considerations show that traumatizing events do not contribute to the occurrence of phobias.
The statement 'The reasoning in the psychiatrist's argument is most vulnerable to criticism on the grounds that the argument takes for granted that a type of phenomenon contributes to the occurrence of another type of phenomenon only if phenomena of these two types are invariably associated' is true.