A group of known smokers are sent literature on the harmful effects of smoking on a weekly basis for one year. At the end of the year, a poll is taken to see how many of the smokers stopped smoking during the year. The results are used to establish the effectiveness of this literature campaign in encouraging smokers to stop smoking.
a. This is an example of what kind of experiment design?
b. What are the potential hazards in drawing the above conclusion from this type of experiment?