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The article "Modeling Sediment and Water Column Interactions for Hydrophobic Pollutants" (Water Research [1984]: \(1169-1174\) ) suggests the uniform distribution on the interval from \(7.5\) to 20 as a model for \(x=\) depth (in centimeters) of the bioturbation layer in sediment for a certain region. a. Draw the density curve for \(x\). b. What is the height of the density curve? c. What is the probability that \(x\) is at most 12 ? d. What is the probability that \(x\) is between 10 and 15 ? Between 12 and 17 ? Why are these two probabilities equal?

Short Answer

Expert verified
For the uniform distribution, the density curve would be a rectangle, with height \(0.08\). The probability that \(x\) is at most \(12\) is \(0.36\), and both probabilities that \(x\) is between \(10\) and \(15\) and between \(12\) and \(17\) are \(0.4\). These two probabilities are equal due to the uniform nature of the distribution and the equal lengths of the intervals.

Step by step solution

01

Draw the Density Curve

In a uniform distribution, all outcomes are equally likely; therefore, the density curve is a rectangle, with the height determined by the requirement that the total area under the curve must be equal to 1.
02

Compute the Height of the Density Curve

The height (h) of a uniform density curve is \(1 / \text{{width of the distribution}}\). So the height is \(1 / (20 - 7.5) = 0.08\).
03

Compute Probability that \(x\) is at most 12

The probability is given by the area under the density curve from \(7.5\) to \(12\). In a uniform distribution, this is simply the base times height of the rectangle formed, i.e., \((12 - 7.5) * 0.08 = 0.36\).
04

Compute Probalities for Given Ranges

The probability that \(x\) is between \(10\) and \(15\) is calculated by \((15-10)*0.08 = 0.4\). The probability that \(x\) is between \(12\) and \(17\) is calculated similarly by \((17-12)*0.08 = 0.4\). The probabilities are equal because the distribution is uniform and the lengths of the intervals are equal too.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Density Curve
The density curve is a graphical representation of the probability distribution of a continuous random variable. Think of it as a smooth outline that shows how the values of the variable are distributed over all possible values. For a uniform distribution, the density curve is particularly simple; it's a flat line, indicating that each value within a specified range has an exactly equal chance of occurring.

When modeling real-world phenomena like the sediment layer's depth, visualizing data through a density curve provides a clear and immediate understanding. It presents at a glance what's happening, rather than having to digest numbers and equations. In our case, drawing this density curve involves sketching a rectangle with a base from 7.5 cm to 20 cm and a height that ensures the area under the curve—representative of the probability—is equal to 1. Understanding this visual tool can significantly boost comprehension of data distribution, an essential element in statistics.
Probability Computation
Centre your thinking on probability as a measure of how likely an event is to occur. Computation of probability often involves area under a curve in continuous distributions. This area corresponds to the likelihood, or the probability, of certain events.

In uniform distributions, this calculation simplifies to a basic arithmetic operation involving the rectangle's width and height (the density). For instance, finding the probability that the depth of bioturbation layer 'x' being at most 12 cm can be visualized as computing the area of a section of our density curve. When put into practice, this simplifies to multiplying the section's width (from 7.5 to 12 cm) by the curve's uniform height (0.08), giving the probability of 0.36, or 36%. By mastering simple probability computations, students can apply these principles to a multitude of problems, from homework exercises to real-world situations.
Bivariate Data Analysis
While not directly illustrated in this problem, understanding bivariate data analysis can deepen your statistical insight. It involves analyzing two variables simultaneously to determine the empirical relationship between them. For example, if our study expanded to include a second variable, like the concentration of a pollutant at different depths, we'd be entering the realm of bivariate analysis.

Techniques include plotting the data points on a scatterplot to identify patterns or trends and using statistical methods to quantify the strength and type of the relationship. This type of analysis is vital when working with datasets where the behavior of two distinct yet connected variables is at play. Although we dealt with a univariate situation here (just a single variable - depth of bioturbation layer), grasping the principles of bivariate data analysis provides a foundation for tackling more complex statistical models.

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