Radiometric dating pretest

09 Mar

are just what the name implies -- new strains that are formed by combining features of more established designs.There are lots of variations that could be constructed from standard design features. I'm featuring these because they illustrate especially well how a design can be constructed to address specific threats to internal validity.By explicitly including testing as a factor in the design, we are able to assess experimentally whether a testing threat is operating. Let's look at a couple of possible outcomes from this design.The first outcome graph shows what the data might look like if there is a treatment or program effect and there is no testing threat.

You might think of this as two pre-post treatment-control designs grafted together.

But both treatment groups clearly outscored both controls. Now, look at a result where there is evidence of a testing threat.

In this outcome, the pretests are again equivalent (because the groups were randomly assigned).

Similarly, the two control groups scored about the same on the posttest.

Thus, the pretest did not appear to affect the outcome.