ResearchMethods: Experiments: How to Design an Experiment (W14-P2) Sp15

If you wanted to do an experiment, there are three general ways for doing it.

First, a quick question: Based on name alone, which do you think is the worst form of experimental design?  Why?

Now let's look at each.

The diagrams in these slides explain how to do the different types of experimental designs.

Read these slides from left to right, starting with the random assignment of subjects into the treatment and control groups.  For each design, what are the steps after the random assignment?  That is, how do you do these types of experiments?

So, Post-test ONLY Control is a good design, but there is a problem.  Are we sure that the IV caused a change in the DV?  How would a pre-test help?

Again, this is a good experimental design.  However, there is a potential problem with this too.  Before the pre-test helped.  Now, the pre-test could be a problem.  How's it a problem?

How does the Solomon Four Group design help control for the possible influence of the pre-test?

The above designs are sub-types of full experiments with one independent variable.

However, what if you wanted to have more than on IV in your study?  How would you design an experiment for that?

Now, let's wrap up with a look at the "worst" designs.

Non-equivalent control group?

If these are the "worst" designs why are we talking about them?  When would you use them?  Better than nothin'?

Which is better a quasi-experimental design or a pre-experimental design?  Why?  What standard are you using to judge whether one is "better" than another?

Speaking of experiments, catch the film reference in the last slide?

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