Curvilinear prediction of posttraumatic growth on quality of life: a five-wave longitudinal investigation of breast cancer survivors.

Abstract

Do cancer survivors experience positive changes (i.e., posttraumatic growth; PTG) resulting in better quality of life? The issue has yet to yield consistent notions. This longitudinal study extends the literature on the role of PTG by examining the curvilinear relationship between PTG and Health-Related Quality of Life (HRQoL), and explored whether PTG predicts subsequent HRQoL in a quadratic relationship across 2years following surgery. Women with breast cancer (N = 359; Mage = 47.5) were assessed at five waves over two years. On every measurement occasion, PTG measured by the posttraumatic growth inventory and HRQoL measured by SF-36 were assessed. The five waves reflect major medical demands and related challenges in the breast cancer trajectory, in which 1-day, 3months, 6months, 12months, and 24months after surgery were adopted as the survey timing. In a series of hierarchical linear modeling (HLM) analyses, the time-lagged predictions of PTG (i.e., linear, quadratic) on HRQoL were examined, controlling demographic and medical covariates. The results revealed that the quadratic term of PTG consistently significantly predicted physical and mental health quality of life (PCS and MCS), while the linear term of PTG did not significantly predict PCS or MCS. With multi-wave longitudinal data, this study demonstrated that the relationship between PTG and HRQoL is curvilinear, and this finding extends to PTG's prediction of subsequent HRQoL. The quadratic relationship has critical implications for clinical assessment and intervention. Details are discussed.