Answer: Differential Selection
Explanation: Differential Selection this is a selection threat with greatest concern when subjects cannot be randomly assigned to a treatment group, particularly if the groups had being unequal when the relevant variables were being considered before treatment intervention. By giving each participant pencils and stickers she is decreasing the threat of differential selection.
Answer: they got beaten and killed by other prisneners
Explanation:
Locked Doors, Highways, Hallways, Panama Canal (Central America)