In a study published in 2015, Bansel et al. found that long-lived C. elegans mutants exhibited a higher proportion of life in an unhealthy state compared to non-mutants. In their 2017 publication, Rollins et al. sought to better understand the relationship between lifespan and quality of life in C. elegans mutants. The authors used two models to assess health span in short-lived mutants: one focused on age-dependent factors such as locomotion, maximum bending amplitude, and thermo-tolerance; the other examined the effects of extrinsic forces over time, including accumulation of autofluorescence and pharyngeal pumping.