For each of the following types of experimental designs (a) give an example, and (b) indicate what threats to validity are controlled. ■             Randomized, posttest-only, control-group design...

For each of the following types of experimental designs (a) give an example, and (b) indicate what threats to validity are controlled.

■             Randomized, posttest-only, control-group design

■             Randomized, pretest-posttest, control-group design

■             Multilevel, completely randomized, between-subjects design

As the course teaching assistant, you are to explain the F-ratio. Define all of its components, and explain the logic of the F-test.