| Preoperational Years | Operational Years | ||||
| Year | Within 8 km | Beyond 8 km | Year | Within 8 km | Beyond 8 km |
| 1962 | 3.3 | 3.3 | 1967 | 2.6 | 3.2 |
| 1963 | 3.4 | 3.4 | 1968 | 2.4 | 3.1 |
| 1964 | 3.0 | 3.1 | 1969 | 2.0 | 2.9 |
| 1965 | 2.9 | 2.9 | 1970 | 2.3 | 3.2 |
| 1971 | 2.3 | 3.1 | |||
| 1972 | 2.1 | 2.9 | |||
| 1973 | 1.9 | 2.6 | |||
| 1974 | 2.2 | 2.8 | |||
| 1975 | 2.0 | 2.9 | |||
To test whether there is a significant difference between tree growth close to and far from the plant site before the plant began operation, use
The results should be
Paired t-test
data: before.close and before.far
t = -1.633, df = 4, p-value = 0.1778
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-0.10800874 0.02800874
sample estimates:
mean of the differences
-0.04
There is no evidence of a difference (though keep in mind that the
sample size is quite small).
To test whether grown is loser close to the plant in the years the plant was operational, use
The results are
Paired t-test
data: after.close and after.far
t = -17.9252, df = 8, p-value = 4.809e-08
alternative hypothesis: true difference in means is less than 0
95 percent confidence interval:
NA -0.6970915
sample estimates:
mean of the differences
-0.7777778
These is very strong evidence for lower growth near the plant in the
years of plant operation.
Try some examples of your own in the work area below.