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WebED Education, Outreach and TrainingA Short Course: Using Modeling and StatisticsVisualization Many people find it difficult to look at a set of numbers and recognize the relationships between them - even if those relationships are very strong. The more numbers there are, the more overwhelmed the observer becomes in trying to discern those relationships. Visualization includes all of the techniques that can be used to convert numeric representations into graphical formats contributing to the understand of the underlying relationships. There are a range of possible techniques from simple graphs to time-sequence animations to dynamic animations and video. To illustrate we will examine a spreadsheet showing the relationship between the dissolved oxygen of the water with the disharge of organic wastes from sewage treatment plants and industry. The organic wastes are measured using a variable called Biochemical Oxygen Demand or BOD. It is a laboratory test which measures how much oxygen might be used up as bacteria decompose the organic waste. A further definition can be found at one of the water quality data sites. Click here to see that site. Other indicators of water quality are defined here. There are also biological measure of water quality defined here. Download the spreadsheet for the Hocking River by clicking here. Use Excel to open up the spreadsheet and look at the BaseData sheet. The last three columns show the date of a sample, the dissolved oxygen, and BOD. We can make an initial hypothesis about the relationship between the two variables. Based on the information above, what should that hypothesis be? After you have formulated the hypothesis click here to see if it matches what the instructors think it should be. Now look at the data in the spreadsheet. Is the hypothesis confirmed for the times when both variables were collected? You should notice that there is not a consistent movement of both variables at the same time. Now let's look at the graph of the DO variable over time. This is shown on the chart1 sheet of the spreadsheet. Notice how it goes up and down over time. Visually what might we expect if we overlaid the graph of the BOD? After you have thought about that, open the chart2 sheet and see the actual relationship. Now we can see that our original hypothesis was actually correct. What we may not have seen is that there is time delay between a larger BOD load and the lower dissolved oxygen level. The graphic helped us to see that relationship. Another kind of visualization that may be important looks at relationships over space rather than over time. One of the biological measures pointed to earlier can be used to illustrate those spatial relationships. The IBI is a measure of fish diversity that is the higher the number the more different species of fish we find in the river. Greater diversity is only possible when there are a minimum of pollution stresses in the stream. So as pollution levels and the number of pollution sources go up, we would expect the IBI to go down. Examine the map below. Is this hypothesis confirmed?
Please contact Al-Azad Iqbal or Steve Gordon for Questions and Comments - Updated 10/2/07 |
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