The concentration of carbon dioxide (CO2) in the atmosphere is increasing rapidly due to our use of fossil fuels. Because plants use CO2 to fuel photosynthesis, more CO2 may cause trees and other plants to grow faster. An elaborate apparatus allows researchers to pipe extra CO2 to a 30-meter circle of forest. We want to compare the growth in base area of trees in treated and untreated areas to see if extra CO2 does in fact increase growth. We can afford to treat three circular areas
(a) Describe the design of a completely randomized experiment using 6 well-separated 30-meter circular areas in a pine forest. Sketch the circles and carry out the randomization your design calls for.
If you used line 101 of Table B in your experiment, which areas would be treated? (Select all that apply.)
1
2
3
4
5
6
7
8
9

(b) Areas within the forest may differ in soil fertility. Describe a matched pairs design using three pairs of circles that will reduce the extra variation due to different fertility. Sketch the circles and carry out the randomization your design calls for.
If you used line 125 of Table B in your experiment, which areas would be treated? (Use odds for the first area in each pair and evens for the second area. Select all that apply.)
the first area in the first pair the first area in the second pair the first area in the third pair
the second area in the first pair the second area in the second pair the second area in the third pair