Colonna and Newman thoroughly review Freud's observations on siblings, as well as those of Klein, Winnicott, Jacobson, Greenacre, and others. They recommend that investigators study sibling transferences in analysis; the development-enhancing effects of characteristic sibling play, sibling admiration, and social modeling; and atypical variations of the sibling experience, such as the effects of separation from and loss of a sibling and the experience of the physically ill or handicapped sibling.