Assignment
1. The following data were collected on the number of Chinook salmon counted in 100m sections of a stream in Clark County.
| Section | Number Salmon |
| 1 | 2 |
| 2 | 3 |
| 3 | 5 |
| 4 | 1 |
| 5 | 0 |
| 6 | 2 |
| 7 | 4 |
| 8 | 1 |
| 9 | 2 |
| 10 | 6 |
| 11 | 2 |
Answer the following questions with respect to this data set:
Using alpha = 0.05, what is the power of these data to estimate the mean salmon density (no./100m) to within 1 fish/m?
Using alpha=beta=0.10 what difference in fish abundance can be detected between two subsequent samples?
2. Two surveys were conducted on a mud flat before and after an oil spill. Conduct a 2-sample t-test of the data using the data below using alpha=0.10 and interpret the results.
| Sample | Before | After |
| 1 | 15 | 8 |
| 2 | 12 | 12 |
| 3 | 8 | 7 |
| 4 | 18 | 15 |
| 5 | 10 | 7 |
| 6 | 19 | 16 |
| 7 | 17 | 20 |
| 8 | 8 | 6 |
| 9 | 22 | 13 |
| 10 | 8 | 3 |
| 11 | 18 | 11 |
Answer the following questions with respect to this data set:
Using alpha=beta=0.10 calculate the minimum detectable difference (MDD or effect size) of the test.
Using the same error rates calculate the sample size needed to detect the observed differences
3. A survey was done to determine the abundance of endemic plants found in an old growth forest. A total of 10 quadrats were sampled and the mean percent cover of the plants in all quadrats was 20.3% with a standard deviation of 12.7.
A) Using Mapstone's decision criteria discussed in class calculate the alpha and beta that would result from a 2-sample t-test to detect a change in 5% plant cover between surveys.
B) With alpha = beta = 0.10 calculate the sample size needed to detect the stated change.
C) Create a MDD-sample size plot and recommend a sample size based on a cost-benefit approach.
This assignment is due next Wednesday, Oct.7, in class.