Question

1. A forester in Vanderhoof, B.C., needs to run a tree growth experiment to understand the effect of brushing (removing unwanted non-commercial tree species that can compete for moisture, nutrients, and sunlight) on the growth of commercially valuable balsam, fir, pine, and spruce trees from seedlings started in the research nursery. Available to her are sixteen different experimental plots northwest of Vanderhoof. Design an experiment for her. (Sec. 3.2)

1. State the response variable.

2. State the number of factors and levels per factor are in your design.

3. How is repetition achieved in your design?

4. How do you use randomization in your design to control for the effects of lurking variables?

5. Sketch a layout of the factors and levels.

Answer 1

a) Here the response variableis the growth of the tree.

b) The number of factors are brushing to compete for moisture,brushing to compete for nutrients, brushing to compete for sunlight. Each of these factors will be applied on balsam, fir, pine and spruce trees.

c) Here she has 16 plots available. Divide the 16 plots into four blocks.She can decide to brush randomly any four for moisture, any four for nutrients and any four for sunlight. and leave the remaining four unbrushed (control group).

Use random number table to select a number form 1 to 4. If you get 3, use that plot for planting tree that is planning to have a brushing to compete for sunlight. If the number is 1, use that plot for planting a tree that is planning to have a brushing for moisture, if you get number 2 use brushing for nutrients and if the number is 4 leave that plot for planting a tree which is going to be left unbrushed.

Repeat this for the other three blocks also.

Trees BLocks	balsam	fir	pine	spruce
I	2	1	3	4
II	1	2	3	4
III	4	3	1	2
IV	3	4	2	1

1- for moisture,    2-for nutrients,   3-sunlight and   4- is unbrushed