1. ASAE Standards, 32nd Ed. S318.10. Tractor roll-over protection;American Society of Agricultural Engineers [ASAE].,1985
2. Farm tractor safety in Kentucky, 1995;Browning;Public Health Reports,1999
3. Sampling techniques, chapter 5: Stratified random sampling;Cochran,1977
4. Tractor risk abatement and control: The policy conference, September 10–12;Donham,1998