Scenario 4 - Effect of Chemical Pollution on Tadpole Growth Experiment Mr. Hasty's twelfth grade class is studying the effect nutrient run-off on stream fish development. His class set up two artificial ponds, one along a natural stream in the forest next to the school and the other in a storm water pond below the football field. Water quality testing of these two water sources indicates a higher level of nitrogen (fertilizer) in the storm water pond (treatment) than in the adjacent natural stream (control). Both artificial ponds were plumbed with PVC drain pipes to receive surface water when it rains either from the natural stream or from the storm water pond. After a large spring rain that filled up both artificial ponds, 100 minnow eggs were collected from the natural stream and were divided evenly (50 eggs each) into the control and treatment artificial ponds. After two weeks both artificial ponds were drained and the size of each remaining minnow (snout-vent length) was measured to the nearest 0.1 mm. The students hypothesized that water that filled the treatment pond would have higher levels of nitrogen pollution from the football field due to the high level of fertilizer used and thus, would inhibit the growth of minnows when compared to those in control pond with natural stream water (H). The independent variable is pond treatment and is categorical with two levels (fertilized field vs. natural forest). The dependent variable is minnow size in mm and is continuous. The observations are unpaired and independent of one another. However, due to differences in the sample sizes between treatments, we must assume unequal variances in our comparison of means. Class Data for the Effect of Nitrogen Run-off on the Minnow Growth Experiment Forest Minnows Size (mm) Fertilized Field Minnow Size (mm) 15.2 16.3 14.2 14.2 16.9 13.2 12.6 10.2 13.6 9.8 9.4 13.9 11.9 10.5 10.6 13.4 17.3 14.2 16.8 15.4 14.2 16.3 12.0 10.9 Forest Minnows Size (mm) Fertilized Field Minnow Size (mm) 15.2 16.3 14.2 14.2 16.9 13.2 12.6 10.2 13.6 9.8 9.4 13.9 11.9 10.5 10.6 13.4 17.3 14.2 16.8 15.4 14.2 16.3 12.0 10.9 13.3 7.5 10.3 11.4 14.6 15.2 12.9 11.1 10.6 12.8 16.0 10.5