Comparative Study of Grief Intensity in Bereaved Monozygotic and Dizygotic Twins
Authors:Jamie L. Graham, Jaime A. Munoz, Jaimee E. Munson, Nancy L. Segal, Jorge L. Torres
Mentor:Nancy L. Segal, Professor of Psychology, California State University Fullerton
The present study investigated bereavement following the loss of a twin and non-twin relatives. A Twin Loss Survey was completed by MZ (monozygotic, identical) twins and DZ (dizygotic, fraternal) twins sampled primarily from the Twinless Twins Support Group International. This group was established in 1987 to meet the emotional needs of bereaved twins. The data were examined in the context of evolutionary psychological theory. The study predicted that (1) MZ twin grief would be greater at the time of loss than DZ twin grief because intensity is expected to correlate positively with greater genetic relatedness, and (2) the loss of a twin would lead to greater grief than the loss of a non-twin relative because of reduced genetic relatedness. The mean age at loss for the MZ twins (n=472) was 47.4 years (SD=15.8) and 45.2 years (SD=15.3) for the DZ twins (n=228). The mean loss interval, defined as participants’ current age minus age at loss, was 6.7 years (SD=8.9) for MZ twins and 6.4 (SD=8.8) for DZ twins. The Grief Intensity Scale (1=No Grief to 7=Total Devastation/Suicide Point) was used to assess degree of bereavement. A t-test demonstrated significantly higher grief ratings for MZ twins (n=467) than for DZ twins (n=227) [t(412.6)=2.3, p<.05, effect size r=.11]. Paired t-tests (ns=6-330) showed that grief at the loss of a twin was rated significantly higher than grief at the loss of all other relatives and non-relatives (p<.001, Cohen’s d=.89-2.84) except for the spouse. Female twins (n=518) expressed significantly higher grief at the loss of a twin than male twins (n=186) [t(300.4)=-3.1, p<.01, effect size r=.18]. A twin-child comparison was omitted due to too few cases. This study enhances understanding of theoretical and applied perspectives on bereavement by identifying associations between genetic relatedness and grief, and demonstrating that individuals grieve differently for different relatives.