Enteroliths are calcifications that form in the gut of horses. The stones can cause considerable morbidity and mortality. A study was conducted to investigate factors (such as diet and environment) that may be related to the formation of enteroliths. Housing is a variable that is coded " 11 " for horses that live in a stall, " 22 " for horses that have access to a small paddock, " 33 " for horses that have a large paddock, " 44 " for horses that live in pasture, and " 55 " for other housing. Housing is a: