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A regression analysis is carried out with \(y=\) temperature, expressed in \({ }^{\circ} \mathrm{C}\). How do the resulting values of \(\hat{\beta}_{0}\) and \(\hat{\beta}_{1}\) relate to those obtained if \(y\) is reexpressed in \({ }^{\circ} \mathrm{F}\) ? Justify your assertion. [Hint: new \(y_{i}=y_{i}^{\prime}=1.8 y_{i}+32\).]

Short Answer

Expert verified
The slope \( \hat{\beta}_1 \) becomes \( 1.8 \hat{\beta}_1 \), and the intercept \( \hat{\beta}_0 \) becomes \( 1.8 \hat{\beta}_0 + 32 \).

Step by step solution

01

Understanding the Conversion Formula

First, let's recall the formula for converting temperatures from Celsius to Fahrenheit: \[ y_i' = 1.8 y_i + 32 \] where \( y_i \) is the temperature in Celsius and \( y_i' \) is the temperature in Fahrenheit.
02

Regression Equation without Conversion

In the initial regression, we have:\[ y = \hat{\beta}_0 + \hat{\beta}_1 x \]where \( y \) is in degrees Celsius, \( x \) is the independent variable, \( \hat{\beta}_0 \) is the intercept, and \( \hat{\beta}_1 \) is the slope.
03

Substituting the Conversion Formula

To express the regression equation in terms of Fahrenheit, substitute \( y_i' = 1.8 y_i + 32 \) into the regression equation:\[ y_i' = 1.8(\hat{\beta}_0 + \hat{\beta}_1 x) + 32 \]
04

Applying Distribution

Distribute the \(1.8\) to both terms inside the parenthesis:\[ y_i' = 1.8 \hat{\beta}_0 + 1.8 \hat{\beta}_1 x + 32 \]
05

Comparing New Parameters

Compare with the original regression form: \( y_i' = \hat{\beta}_0' + \hat{\beta}_1' x \). Thus, we determine the new coefficients:- \( \hat{\beta}_0' = 1.8 \hat{\beta}_0 + 32 \) (new intercept)- \( \hat{\beta}_1' = 1.8 \hat{\beta}_1 \) (new slope)
06

Conclusion About the Coefficient Changes

The slope \( \hat{\beta}_1 \) is scaled by 1.8, and the intercept \( \hat{\beta}_0 \) is scaled by 1.8 and then adjusted by adding 32. Hence, both coefficients change according to the conversion formula and the linearity of the transformations.

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Key Concepts

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

Temperature Conversion
Understanding temperature conversion between Celsius and Fahrenheit is crucial in many scientific and practical applications. The formula to convert temperatures from Celsius to Fahrenheit is given by: \[ y' = 1.8y + 32 \] This tells us that to convert a temperature from Celsius \( (y) \) to Fahrenheit \( (y') \), we multiply the Celsius temperature by 1.8 and then add 32 degrees. This formula reflects two fundamental operations: scaling (multiplication by 1.8) and translation (adding 32). - **Scaling by 1.8** keeps the change proportional, as Fahrenheit degrees are larger compared to Celsius. - **Adding 32** shifts the scale to incorporate the offset between the two temperature systems. This conversion is essential whenever comparing or converting temperature-dependent observations between these two units.
Regression Coefficients
In regression analysis, coefficients like \( \hat{\beta}_0 \) and \( \hat{\beta}_1 \) serve as critical components in modelling relationships. The intercept \( \hat{\beta}_0 \) represents the expected value of the dependent variable when all independent variables are zero. Meanwhile, \( \hat{\beta}_1 \) is the slope of the regression line, showing how much the dependent variable is expected to increase (or decrease) with each unit increase in the independent variable. - **Intercept \( \hat{\beta}_0 \)**: Initial value or starting point of the regression line. - **Slope \( \hat{\beta}_1 \)**: Reflects the rate of change. When a dependent variable undergoes transformations, like changing temperature units, these coefficients also adjust. If converting Celsius to Fahrenheit, the new slope \( \hat{\beta}_1' \) becomes \( 1.8 \times \hat{\beta}_1 \) because the range of temperatures in Fahrenheit is broader. The intercept, \( \hat{\beta}_0' \), not only scales by 1.8 but also adjusts by 32 to account for differences in base units.
Linear Transformations
Linear transformations, such as \( y' = 1.8y + 32 \), play a pivotal role in adapting regression models for diverse measurement scales. By converting temperature scales, we notice how these linear transformations can predictably alter our regression coefficients. - **Impact on the slope**: Because transformations like scaling a unit impacts how rapidly values change, the slope \( \hat{\beta}_1 \) reflects this through multiplication by the scaling factor. Thus, \( \hat{\beta}_1' = 1.8 \times \hat{\beta}_1 \). - **Impact on the intercept**: Besides scaling, a constant like 32 changes the initial displacement or position, thus \( \hat{\beta}_0' = 1.8 \hat{\beta}_0 + 32 \). Using these linear transformations helps us understand and adjust regression models for compatibility with varied datasets, retaining relationships while modifying measurement units. They ensure that our regression outcomes still provide meaningful insights, no matter how our measurement scales shift.

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Most popular questions from this chapter

As the air temperature drops, river water becomes supercooled and ice crystals form. Such ice can significantly affect the hydraulics of a river. The article "Laboratory Study of Anchor Ice Growth" (J. Cold Regions Engrg., 2001: 60-66) described an experiment in which ice thickness \((\mathrm{mm})\) was studied as a function of elapsed time ( \(\mathrm{hr}\) ) under specified conditions. The following data was read from a graph in the article: \(n=33 ; x=.17, .33, .50, .67, \ldots, 5.50\); \(y=.50,1.25,1.50,2.75,3.50,4.75,5.75,5.60\), \(7.00,8.00,8.25,9.50,10.50,11.00,10.75,12.50\), \(12.25,13.25,15.50,15.00,15.25,16.25,17.25\), \(18.00,18.25,18.15,20.25,19.50,20.00,20.50\), \(20.60,20.50,19.80\). a. The \(r^{2}\) value resulting from a least squares fit is \(.977\). Given the high \(r^{2}\), does it seem appropriate to assume an approximate linear relationship? b. The residuals, listed in the same order as the \(x\) values, are $$ \begin{array}{rrrrrrr} -1.03 & -0.92 & -1.35 & -0.78 & -0.68 & -0.11 & 0.21 \\ -0.59 & 0.13 & 0.45 & 0.06 & 0.62 & 0.94 & 0.80 \\ -0.14 & 0.93 & 0.04 & 0.36 & 1.92 & 0.78 & 0.35 \\ 0.67 & 1.02 & 1.09 & 0.66 & -0.09 & 1.33 & -0.10 \\ -0.24 & -0.43 & -1.01 & -1.75 & -3.14 & & \end{array} $$ Plot the residuals against \(x\), and reconsider the question in (a). What does the plot suggest?

The article "Promoting Healthy Choices: Information versus Convenience" (Amer. Econ. J.: Applied Econ., 2010: 164 - 178) reported on a field experiment at a fast-food sandwich chain to see whether calorie information provided to patrons would affect calorie intake. One aspect of the study involved fitting a multiple regression model with 7 predictors to data consisting of 342 observations. Predictors in the model included age and dummy variables for gender, whether or not a daily calorie recommendation was provided, and whether or not calorie information about choices was provided. The reported value of the \(F\) ratio for testing model utility was \(3.64\). a. At significance level .01, does the model appear to specify a useful linear relationship between calorie intake and at least one of the predictors? b. What can be said about the \(P\)-value for the model utility \(F\) test? c. What proportion of the observed variation in calorie intake can be attributed to the model relationship? Does this seem very impressive? Why is the \(P\)-value as small as it is? d. The estimated coefficient for the indicator variable calorie information provided was \(-71.73\), with an estimated standard error of \(25.29\). Interpret the coefficient. After adjusting for the effects of other predictors, does it appear that true average calorie intake depends on whether or not calorie information is provided? Carry out a test of appropriate hypotheses.

Suppose that in a certain chemical process the reaction time \(y\) (hr) is related to the temperature \(\left({ }^{\circ} \mathrm{F}\right)\) in the chamber in which the reaction takes place according to the simple linear regression model with equation \(y=5.00-.01 x\) and \(\sigma=.075\). a. What is the expected change in reaction time for a \(1^{\circ} \mathrm{F}\) increase in temperature? For a \(10^{\circ} \mathrm{F}\) increase in temperature? b. What is the expected reaction time when temperature is \(200^{\circ} \mathrm{F}\) ? When temperature is \(250^{\circ} \mathrm{F}\) ? c. Suppose five observations are made independently on reaction time, each one for a temperature of \(250^{\circ} \mathrm{F}\). What is the probability that all five times are between \(2.4\) and \(2.6 \mathrm{~h}\) ? d. What is the probability that two independently observed reaction times for temperatures \(1^{\circ}\) apart are such that the time at the higher temperature exceeds the time at the lower temperature?

Suppose that \(x\) and \(y\) are positive variables and that a sample of \(n\) pairs results in \(r \approx 1\). If the sample correlation coefficient is computed for the \(\left(x, y^{2}\right)\) pairs, will the resulting value also be approximately 1? Explain.

Infestation of crops by insects has long been of great concern to farmers and agricultural scientists. The article "Cotton Square Damage by the Plant Bug, Lygus hesperus, and Abscission Rates" (J. Econ. Entomol., 1988: 1328-1337) reports data on \(x=\) age of a cotton plant (days) and \(y=\%\) damaged squares. Consider the accompanying \(n=12\) observations (read from a scatter plot in the article). $$ \begin{array}{l|rrrrrr} x & 9 & 12 & 12 & 15 & 18 & 18 \\ \hline y & 11 & 12 & 23 & 30 & 29 & 52 \\ x & 21 & 21 & 27 & 30 & 30 & 33 \\ \hline y & 41 & 65 & 60 & 72 & 84 & 93 \end{array} $$ a. Why is the relationship between \(x\) and \(y\) not deterministic? b. Does a scatter plot suggest that the simple linear regression model will describe the relationship between the two variables? c. The summary statistics are \(\sum x_{i}=246\), \(\sum x_{i}^{2}=5742, \quad \sum y_{i}=572, \quad \sum y_{i}^{2}=35,634\) and \(\sum x_{i} y_{i}=14,022\). Determine the equation of the least squares line. d. Predict the percentage of damaged squares when the age is 20 days by giving an interval of plausible values.

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