For each of the following designs (a) give an example, (b) identify the major threats to validity, and (c) state the limits on the conclusions that can be drawn. ■             Single-group,...

For each of the following designs (a) give an example, (b) identify the major threats to validity, and (c) state the limits on the conclusions that can be drawn.

■             Single-group, posttest-only design

■             Ex post facto design

■             Single-group, pretest-posttest design

■             Pretest-posttest, natural control-group design

Does a high between-groups variance in an experiment provide sufficient evidence to conclude that the independent variable affected the dependent variable? Explain.