Researchers were interested in researching factors deemed to be of interest for extending human lifespan. One of those factors was hypothesized to be the intake of water. The experiment was designed as follows:

20 people were put into a room and given a liter of water each. They were told they would stay in the room for 50 years without any outside interference and, after the end of the 50 years, researchers would come back to check on them. 50 years later when the researchers returned to the room, all 20 individuals were deceased. Thus, the researchers concluded that water is deadly.

Answer the following questions:

1) (worth 1 point) - what is the dependent variable in this study?

2) (worth 1 point) - what is the independent variable in this study?

3) (worth 3 points) - what is needed for the conclusion to be valid in this study?

4) (worth 3 points) - Describe in specific detail how the researchers could have/should have designed the study in order for them to be able to conclude the validity of the conclusion?