Why is it important to rule out the threats to internal validity? What could be the consequences if an evaluator is unable to rule out all or most of the threats to internal validity? Why are...

Why is it important to rule out the threats to internal validity? What could be the

consequences if an evaluator is unable to rule out all or most of the threats to internal validity?

Why are experimental designs considered the strongest research designs? Do they


have limitations in the context of evaluation and, if so, what are these limitations?