Access to nutritious food is a fundamental pillar of human success, but such access has been unequal throughout history. In pre-industrial European societies, meat was a highly sought-after food, and access to it was often related to a higher social status. The ratios of carbon and nitrogen isotopes in human bone collagen can provide data about what a person ate. Nitrogen isotope ratios reflect the amount of meat a person ate, while carbon isotope ratios reveal what proportion of plants a person ate used the C4 carbon fixation photosynthesis pathway, from which one can infer how much low-status millet and variable-status marine foods a person may have consumed. However, comparing isotope ratios across sites is difficult; the use of manure fertilizer, varying climate conditions, and undernourishment can change the context in which raw values are interpreted. Rozenn Colleter, Michael P. Richards, and colleagues work around this constraint by using the interdecile ratio.