Hennington pond was the only pond on the FIU campus not treated with chemicals o

Question

Hennington pond was the only pond on the FIU campus not treated with chemicals or subjected to storm run-off. In March 2007, a sewage main ruptured and the lake became contaminated with sewage effluent. You have been provided with data on the Phosphorus levels in Hennington pond for two years 2004 (before perturbation) and 2007 (after perturbation). For both years, sampling was conducted by collecting water samples from 20 random sites within the pond. Based on observations of Hennington pond during 2004 and 2007, we could ask the following question: Has the Phosphorus level in Hennington pond changed between 2004 and 2007? 1. Write a null and alternative ecological hypothesis for this study. 2. Write a null and alternative statistical hypothesis for this study. 3. Are the alternative hypotheses you wrote one-tailed or two-tailed? Why does this matter? 4. What would you set your alpha value at? WHY? 5. After you analyze your data in Excel, you get a p-value of 0.03. What does this mean? 6. Using data given, produce a summary table (do not include raw data) showing the mean

Explanation / Answer

Answer - 4:

Since there is no information given about the level of significance, we need to make a decision on the basis of criticality of type I error which is rejecting the null hypothesis when it is true. In the given scenaario, if we reject the null hypothesis and conclude that there has been a significant change in Phosphorus level from 2004 to 2007 whereas it wasn't actually the case, we would be making type I error and that would lead to unnecessary further actions taken and cost to reduce it. So, we would rather be setting up a low value of alpha as 0.01.

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