5. The ratio of DDE (related to DDT) to PCB concentrations in bird eggs has been

Question

5. The ratio of DDE (related to DDT) to PCB concentrations in bird eggs has been shown to have a number of biological implications. The ratio is used as an indication of the movement of contamination through the food chain. The paper The Ratio of DDE to PCB Concentrations in Great Lakes Herring Gull Eggs and Its Use in Interpreting Contaminants Data [Journal of Great Lakes Research (1998) 24(1):1231 reports the following ratios for eggs collected at 13 study sites from the five Great Lakes. The eggs were collected from both terrestrial- and aquatic-feeding birds. Terrestia 76.50 6.03 3.51 9.96 4.24 7.74 9.54 41.70 1.84 2.50 1.54 Aquat 0.27 0.61 0 0.14 0.63 0.23 0.56 0.48 0.16 0.18 (a) Compute the mean for each group of birds. (b) Compute the 20% trimmed mean for each group. Do these means differ much fron what was calculated in (a)? (c) Compute the first quartile, median, and third quartile for each group (d) Compute the standard deviation for each group. Which group has the highest variability? Try to give a contextual reason for why we would see higher variability in one group versus the other? (e) Using the sample statistics calculated, summarize the difference between the two groups. Some statistics may be useful for comparison, some may not. Use your discretion. You probably only need two or three sentences.

Explanation / Answer

Terrestial Aquatic 76.5 0.27 6.03 0.61 3.51 0.54 9.966 0.14 4.24 0.63 7.74 0.23 9.54 0.56 41.7 0.48 1.84 0.16 2.5 0.18 1.54 Total 165.106 3.8 Mean 15.00964 0.38 20 percent trimmed mean 9.674 0.37875 Quirtile 1 3.005 0.1925 Quirtile 2/Median 6.03 0.375 Quirtile 3 9.753 0.555 Standard deviation 23.32781 0.201108 Coefficient of variation 1.554189 0.529232 b) Yes trimmed mean is different from mean calculated by using all data points. e) Coefficient of variation for Aquatic group is less than for Terristial group. So we can conclued that consistency in Auatic group is more.

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