Image degradation due to head motion is ubiquitous in MRI, reduces sensitivity, hinders clinical diagnosis and increases the risk of spurious findings. The few existing objective measures of degradation are often used sub-optimally, to remove the most degraded datasets from analysis. Using a large dataset (N~1400) we show how to incorporate an validated index of degradation into the analysis of group studies. The benefit is demonstrated for the case of healthy age-related difference in brain relaxometry data using the SPM software. However, the proposed framework is flexible with broad potential, including the analysis of other metrics and body regions.