Statistical Comparison of Multiple Methods for the Determination of Dissolved Oxygen Levels in Natural Waters

The following experiment reinforces students working knowledge of statistics by utilizing the t test to compare the results of two independent methods for the determination of dissolved oxygen (DO). In this experiment students utilize a dissolved oxygen probe to determine the levels of DO in natural waters at two sampling locations while obtaining samples of water from the laboratory for analysis using the classic Winkler titration. The importance of using proper sampling methods and techniques to obtain representative samkples is a large focus of the prelaboratory discussion and is continually stressed during fieldwork. After analyzing the water samples by the DO mete and the Winkler titration, students pool the class data and are asked to determine if the two methods for dissolved oxygen agree at each sampling location. The students are then asked to determine if the DO levels at the different sampling locations are statistically different or not. The students are asked to consider why their results agree or differ from the theoretical value they calculate using Henrys law.