Running an experiment in the basement of Kenneth Taylor Hall with a single group of student volunteers. All volunteers take a short survey that measures their Level of political optimism on a scale of 1-10. You are interested in volunteers who are the most politically optimistic, so you select all those in the initial group who score 10 out of 10 on the political optimism scale: These individuals will be used for your actual experiment (the other volunteers are sent home). Your hypothesis is that negative advertising will have a negative impact on the Level of political optimism expressed by the remaining participants. Accordingly, you show the experimental participants a series of negative ads. With that complete, your volunteers once again take the Level of political optimism survey. You record a decrease in the overall Level of political optimism, which you believe supports your hypothesis. 

1. Which threats to Internal Validity is most obviously present in your experimental design?
2. Differences in the Experimental Environment 
3. History Contingency Effects
4. Regression Effects.

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