Major threats to pioneer life and limb came from accidents, exhaustion, and disease. Crossing rivers were probably the most dangerous thing pioneers did. Swollen rivers could tip over and drown both people and oxen. Such accidents could cause the loss of life and most or all of valuable supplies.
Internal validity would be the extent through which a record an accounting a reliable reason as well as effect correlation among both medications as well as consequence.
Perhaps it speaks to the fact that the original study ends up making it achievable to help reduce possible causes for something like a discovering.
