An analysis of 50 train derailment incidents identified the main causes listed below, where t denotes bad track, e denotes faulty equipment, h denotes human error, and o denotes other causes (based on data from the federal railroad administration). t t t e e h h h h h o o h h h e e t t t e t h o t t t t t t t h t t h e e t t e e t t t h t t o o o construct the relative frequency distribution.