Effect of quality of life on inter-individual differences in the intercept for NKCA. Graphical representation of the relationship between quality of life (FACT-G scores) and natural killer cell activity (NKCA) as estimated by the hierarchical linear model from the time of the initial assessment (i.e., Baseline) to 6 weeks post radiotherapy . The slopes for NKCA were based on differences in quality of life levels, calculated as the average upper and lower quartiles. Greater levels of NKCA at baseline and post-treatment were associated with higher quality of life. *bintercept = 1.9, p = 0.02.