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A European standard value for a low-emission window glazing uses 0.59 as the proportion of solar energy that enters a room. Suppose that the distribution of the proportion of solar energy that enters a room is a beta random variable. a. Calculate the mode, mean, and variance of the distribution for \(\alpha=3\) and \(\beta=1.4\) b. Calculate the mode, mean, and variance of the distribution for \(\alpha=10\) and \(\beta=6.25 .\) c. Comment on the difference in dispersion in the distribution from parts (a) and (b).

Short Answer

Expert verified
The distribution in part (b) is less spread out than in part (a).

Step by step solution

01

Understanding the Beta Distribution

The Beta distribution is defined by two shape parameters, \( \alpha \) and \( \beta \). It is often used to model the distribution of proportions or probabilities. The support of a beta-distributed random variable is the interval \((0, 1)\).
02

Formula for Mode of Beta Distribution

The mode of a Beta distribution for \( \alpha > 1 \) and \( \beta > 1 \) is given by: \[ \text{Mode} = \frac{\alpha - 1}{\alpha + \beta - 2} \]
03

Calculate Mode for Part (a)

Using \( \alpha = 3 \) and \( \beta = 1.4 \):\[ \text{Mode} = \frac{3 - 1}{3 + 1.4 - 2} = \frac{2}{2.4} = \frac{5}{6} \approx 0.8333 \]
04

Calculate Mean for Part (a)

The mean of a Beta distribution is given by:\[ \text{Mean} = \frac{\alpha}{\alpha + \beta} \]Substitute \( \alpha = 3 \) and \( \beta = 1.4 \):\[ \text{Mean} = \frac{3}{3 + 1.4} = \frac{3}{4.4} \approx 0.6818 \]
05

Calculate Variance for Part (a)

The variance of a Beta distribution is given by:\[ \text{Variance} = \frac{\alpha \beta}{(\alpha + \beta)^2 (\alpha + \beta + 1)} \]Substitute \( \alpha = 3 \) and \( \beta = 1.4 \):\[ \text{Variance} = \frac{3 \times 1.4}{(4.4)^2 (5.4)} \approx 0.0452 \]
06

Calculate Mode for Part (b)

Using \( \alpha = 10 \) and \( \beta = 6.25 \):\[ \text{Mode} = \frac{10 - 1}{10 + 6.25 - 2} = \frac{9}{14.25} \approx 0.6316 \]
07

Calculate Mean for Part (b)

Substitute \( \alpha = 10 \) and \( \beta = 6.25 \):\[ \text{Mean} = \frac{10}{10 + 6.25} = \frac{10}{16.25} \approx 0.6154 \]
08

Calculate Variance for Part (b)

Substitute \( \alpha = 10 \) and \( \beta = 6.25 \):\[ \text{Variance} = \frac{10 \times 6.25}{(16.25)^2 (17.25)} \approx 0.0128 \]
09

Comment on Dispersion

The variance for part (a) is larger \( 0.0452 \) compared to that of part (b) \( 0.0128 \). This indicates that the distribution in part (b) is less dispersed and more concentrated around the mean and mode than in part (a).

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Key Concepts

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

Probability Distribution
In statistics, a probability distribution represents the likelihood of a random variable to take on different values. When working with continuous random variables, we express this likelihood as a probability density function (PDF). The Beta distribution is a notable example of a continuous probability distribution used for modeling the behavior of random variables that take values within the interval of 0 and 1, like proportions and probabilities.

With the Beta distribution, two shape parameters, \( \alpha \) and \( \beta \), determine the shape of the distribution. By varying these parameters, you can model a distribution that is uniform, bell-shaped, or skewed in either direction. This flexibility is what makes the Beta distribution a strong tool in various fields, including Bayesian statistics, quality control, and project management.
Statistical Dispersion
Statistical dispersion refers to the spread of a set of values within a dataset or distribution. In the context of a probability distribution like the Beta distribution, we quantify dispersion using variance. Variance indicates how concentrated or spread out the values are around the mean.

For instance, in our exercise, we calculated the variance for the Beta distribution in two instances:
  • \( \alpha = 3 \), \( \beta = 1.4 \), variance \( \approx 0.0452 \)
  • \( \alpha = 10 \), \( \beta = 6.25 \), variance \( \approx 0.0128 \)
The larger variance in the first case suggests a wider spread of values, while the smaller variance in the second case indicates values clustered more tightly around the mean. Understanding how dispersion changes with different parameters helps in modeling and interpreting the uncertainty and reliability of forecasts and experiments.
Mathematical Statistics
Mathematical statistics involves applying mathematical theories and methods to analyze and interpret data. It provides the groundwork for statistical inference which is crucial in making predictions and improving decision-making based on data analysis.

In our exercise, we used mathematical formulas derived from the Beta distribution to compute the mode, mean, and variance. These calculations are key components of descriptive statistics that summarize the essential features of distributions in terms of central tendency (mean), most probable outcome (mode), and variability (variance).

Through these computations, we can elucidate the underlying structure of data, test hypotheses, and predict trends and behaviors with more certainty. Mathematical statistics thus bridges theoretical developments in fields such as probability theory with practical applications in data science, economics, and other disciplines reliant on data-driven insights.
Shape Parameters
Shape parameters like \( \alpha \) and \( \beta \) in the Beta distribution are critical as they dictate the configuration or 'shape' of the probability distribution graph. By altering these parameters, we transform the distribution's characteristics.

For example, small values of \( \alpha \) and \( \beta \) make the distribution more U-shaped, while equal parameters result in a symmetric, bell-shaped distribution. When \( \alpha \) is larger than \( \beta \), the distribution skews to the right, whereas if \( \beta \) is greater, it skews to the left.

In the provided exercise, different sets of \( \alpha \) and \( \beta \) values were used to highlight the differences in mean, mode, and variance, thereby illustrating different probability shapes and their implications on solar energy entrance in a room. Mastering the impact of shape parameters is essential for adeptly tuning distributions to fit observed data or theoretical models.

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