Grace randomly assigns college-bound African-American students to the intervention or to a control condition. Grace gives a mathematics achievement test in September to both groups. Through the academic year the treatment condition receives the intervention. She uses end of year achievement tests to see whether there are differences between conditions. Grace found that students studied together for the end of year achievement tests. She believes that some of the students in the treatment condition shared intervention information with the control group. Which of the following threats does Grace now have to be most concerned about?
◦ Selection by treatment
◦ Maturation by treatment
◦ Statistical regression
◦ Treatment diffusion
Bottom-up control versus top-down control.
African Rodent
A rare albino American alligator
Extinct North American Megafauna
Giant African Earthworm
Endocrine and nervous control of blood pressure.