/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 2 Johnston \(^{44}\) reports on a ... [FREE SOLUTION] | 91Ó°ÊÓ

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Johnston \(^{44}\) reports on a study of 40 firms relating the output to average fixed costs. Instead of using their 40 pieces of data, we use just their array means in the following table. $$ \begin{array}{|l|llllllll|} \hline x & 50 & 160 & 250 & 400 & 650 & 875 & 1250 & 2000 \\ \hline y & 4.6 & 4 & 3.1 & 3.2 & 3.3 & 2 & 2.7 & 2.5 \\ \hline \end{array} $$ Here \(x\) is output in millions of units, and \(y\) is average cost per unit of output (in millions). Use power regression to find the best-fitting power function to the data and the correlation coefficient. Graph.

Short Answer

Expert verified
The best-fitting power function is found to be \( y = ax^b \), with \( a \) and \( b \) determined by linear regression on the log-transformed data. The correlation coefficient \( r \) indicates the strength of fit.

Step by step solution

01

Understanding Power Regression

Power regression is used to fit a model in the form of \( y = ax^b \). We will transform this into a linear form by taking the logarithm of both sides, resulting in \( \log(y) = \log(a) + b \cdot \log(x) \). This transformation allows us to use linear regression methods.
02

Transform the Data

Take the logarithm of both the \( x \) and \( y \) values in our table to transform them for analysis. Specifically, calculate \( \log(x) \) and \( \log(y) \) for each pair of values.
03

Apply Linear Regression to Transformed Data

Use the transformed values \( \log(x) \) and \( \log(y) \) to perform a linear regression. The slope of the line will be \( b \) and the y-intercept will be \( \log(a) \).
04

Calculate Regression Coefficients

From the linear regression of transformed data, determine the values of \( a \) and \( b \). The coefficient \( a \) is obtained by taking the exponential of the y-intercept obtained from regression, and \( b \) is the slope of the line.
05

Calculate Correlation Coefficient

Calculate the correlation coefficient (\( r \)) of the logarithmically transformed data. This will indicate the strength of the relationship between \( x \) and \( y \).
06

Graph the Power Function

Plot the original data along with the power function \( y = ax^b \) on a graph to visualize the fit of the function to the data.

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Key Concepts

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

Average Fixed Costs in Power Regression
Average fixed costs represent the portion of business expenses that do not change with the level of output. These costs include expenses like rent, salaries, and machinery that remain constant regardless of the quantity produced.

In the context of power regression, average fixed costs ( y ) are measured against output ( x ) across different levels. The goal is to understand how costs per unit change as firms increase their production scale. This can help businesses identify efficiencies or potential savings as production increases.

Such analysis may allow firms to plan better by predicting costs behavior as they scale up their operations. The reduced per-unit cost as production increases can be a significant aspect of competitive strategy.
Linear Regression in Power Regression
Linear regression is a statistical method used to examine the relationship between two variables. In power regression, we initially employ a transformation to convert our power model into a linear form.

By transforming the data, we use a straight-line approach to solve problems typically characterized by non-linear relationships. After taking the logarithm of both x (output) and y (average cost), we can express the relationship as \( \log(y) = \log(a) + b \cdot \log(x) \).

Linear regression then provides a straightforward way to estimate the parameters a and b which define the power function. This conversion allows us to mix the simplicity of linear methods with the flexibility needed for modeling real-world scenarios.
Understanding Transformed Data
Data transformation is a crucial process in power regression. It involves converting the original data into a form that is more suitable for analysis. In this exercise, x and y values are transformed by applying a logarithm to fit a linear model.

Transformed data allows us to bypass complex calculations inherent in non-linear relationships. This simplification enables straightforward computation using linear regression techniques.

By transforming x and y into \( \log(x) \) and \( \log(y) \) respectively, we set the stage for linear regression. This step is essential because it makes it easier to interpret and analyze the relationship between output and cost as a linear trend.
Interpreting the Correlation Coefficient
The correlation coefficient, often denoted as r , measures the strength and direction of the linear relationship between two variables. In this task, it helps us understand the fit of the power regression model to the transformed data.

An r value close to 1 or -1 indicates a strong linear relationship. For instance, if r is close to 1, it suggests that as x increases, y also increases in a linear fashion after transformation. If r is close to -1, it implies that when x increases, y decreases.

This coefficient provides insight into how well our model describes the observed data, guiding future predictions and strategic decisions based on the model.

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Most popular questions from this chapter

Economic Entomology Karr and Coats \(^{67}\) studied the effects of several chemicals on the growth rate of the German cockroach. The following table gives their data for the percent of the chemical \(\alpha\) -terpineol in the diet of the cockroach. $$ \begin{array}{|l|ccc|} \hline \text { Percent } \alpha \text { -terpineol } & 1 & 10 & 25 \\ \hline \text { Days to Adult Stage } & 129 & 113 & 115 \\ \hline \end{array} $$ a. On the basis of the data given in the table, find the bestfitting logarithmic function using least squares. Graph. b. Use this model to estimate the days to adult stage with a diet of \(20 \% \alpha\) -terpineol.

Population of Northeast The table gives the population in millions of the northeastern part of the United States for some selected early years. \(^{70}\) a. On the basis of the data given for the years \(1790-1890\), find the best- fitting exponential function using exponential regression. Determine the correlation coefficient. Graph. Using this model, estimate the population in \(1990 .\) b. Now find the best-fitting logistic curve. Graph. Using this model, estimate the population in \(1990 .\) Note that the actual population of the Northeast in 1990 was 50.8 million. $$ \begin{array}{|l|ccc|} \hline \text { Year } & 1790 & 1810 & 1830 \\ \hline \text { Population } & 2.0 & 3.5 & 5.5 \\ \hline \text { Year } & 1850 & 1870 & 1890 \\ \hline \text { Population } & 8.6 & 12.3 & 17.4 \\ \hline \end{array} $$

Ecology Savopoulou-Soultani and coworkers \(^{36}\) collected the data shown in the table relating the number \(y\) of days Lobesia botrana spent in the larvae stage to the percent \(x\) of brewer's yeast in its diet. $$ \begin{array}{|c|ccccccc|} \hline x & 0 & 1.5 & 2.7 & 5.7 & 8.2 & 9.2 & 10.8 \\ \hline y & 33.1 & 28.8 & 27.2 & 27.7 & 26.7 & 30.3 & 29.2 \\ \hline \end{array} $$ a. Use quadratic regression to find \(y\) as a function of \(x\). b. Find the percent of yeast that results in a minimum number of days spent in the larvae stage.

Find the best-fitting straight line to the given set of data, using the method of least squares. Graph this straight line on a scatter diagram. Find the correlation coefficient. $$ (1,4),(2,2),(3,2),(4,1) $$

Population Ecology Wagner \(^{31}\) collected the data found in the following table relating the percent mortality \(y\) of eggs of the sweet-potato whitefly and the temperature \(T\) in degrees Celsius. $$\begin{array}{|c|cccccccc|}\hline T & 20 & 22 & 24 & 26 & 28 & 30 & 32 & 34 \\\\\hline y & 7 & 6 & 3.5 & 5 & 7 & 4 & 6.8 & 18 \\\\\hline\end{array}$$ Use quartic regression to find the best-fitting fourth-order polynomial to the data and the correlation coefficient. Graph.

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