Question

3) You are interested in the effects of coal-fired power plants on local mercury contamination in wetlands. Your funding comes from a local power company that wants 2 of the plants to be their power plants in Illinois. You look at a map and select 2 of their plants and 2 plants that are of similar energy output. You want to know if the power plant is having an effect on mercury concentrations in sediment samples. In addition to what you did above, answer this question: Is power plant a fixed or random effect based on how the question is worded and how did you know?

Plant	Hg
Baldwin	267.84
Baldwin	109.64
Baldwin	289.01
Baldwin	368.21
Baldwin	342.63
Baldwin	447.59
Baldwin	335.2
Newton	251.21
Newton	323.57
Newton	367.29
Newton	199.62
Newton	198.08
Newton	197.21
Newton	208.52
Newton	124.2
Newton	205.03
Joppa	539.48
Joppa	846.37
Joppa	273.13
Joppa	218.83
Joppa	211.6
Joppa	1100
Joppa	308.02
Marion	167.26
Marion	537.42
Marion	303.16
Marion	175.95
Marion	259.87
Marion	232.32
Marion	224.09
Marion	395.69
Marion	376.97

Answer 1

One-way ANOVA: Hg versus Plant1

Method

Null hypothesis         All means are equal
Alternative hypothesis At least one mean is different
Significance level      α = 0.05

Equal variances were assumed for the analysis.

Factor Information

Factor Levels Values
Plant1       4 Baldwin, Joppa, Marion, Newton

Analysis of Variance

Source DF   Adj SS Adj MS F-Value P-Value
Plant1   3   302761 100920     2.95    0.050
Error   28   958140   34219
Total   31 1260901

Model Summary

      S    R-sq R-sq(adj) R-sq(pred)
184.985 24.01%     15.87%       0.00%

Means

Plant1   N   Mean StDev      95% CI
Baldwin 7 308.6 105.2 (165.4, 451.8)
Joppa    7    500    349 ( 356,   643)
Marion   9 297.0 120.6 (170.7, 423.3)
Newton   9 230.5   73.6 (104.2, 356.8)

Pooled StDev = 184.985

F = 2.949239

critical value = 2.946685 at 0.05 significance level

since F > critical value

we reject the null hypothesis

the power plant is having an effect on mercury concentrations in sediment samples.