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The following statement appeared in the article "Dimensions of Adjustment Among College Women" (Journal of College Student Development \([1998]: 364):\) Regression analyses indicated that academic adjustment and race made independent contributions to academic achievement, as measured by current GPA. Suppose $$ \begin{aligned} y &=\text { current GPA } \\ x_{1} &=\text { academic adjustment score } \\ x_{2} &=\text { race (with white }=0 \text { , other }=1) \end{aligned} $$ What multiple regression model is suggested by the statement? Did you include an interaction term in the model? Why or why not?

Short Answer

Expert verified
The multiple regression model is \(y = \beta_0 + \beta_1x_1 + \beta_2x_2 + \epsilon\). There's no need to include an interaction term as the problem states the variables contribute independently to the dependent variable.

Step by step solution

01

Define the variables

Define the given variables in the context of the problem: \(y\) for current GPA, \(x_1\) for academic adjustment score, and \(x_2\) for race where white is represented as 0, and others as 1.
02

Formulate the Regression Model

Form the multiple regression model based on the problem statement using the formula \(y = \beta_0 + \beta_1x_1 + \beta_2x_2 + \epsilon\), where \(y\) is the dependent variable (current GPA), \(\beta_0\) is the y-intercept, \(\beta_1\) and \(\beta_2\) are the coefficients of the independent variables \(x_1\) (academic adjustment score) and \(x_2\) (race), respectively, and \(\epsilon\) represents the error term. Each of the independent variables \(x_1\) and \(x_2\) are contributing independently as mentioned in the problem statement.
03

Decide on the Interaction Term

Determine whether to include an interaction term (\(\beta_3x_1x_2\)) in the model. An interaction term would indicate that the effect of one predictor variable depends on the value of another predictor variable. However, the problem statement says that the variables contribute independently to the GPA score, so the interaction term should not be included.

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Key Concepts

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

Academic Adjustment
Academic adjustment is a crucial factor when examining students' performance in a college setting. It generally refers to how well students adapt to various academic demands. Consider it as the student’s ability to manage their course load, engagement with learning activities, and the overall process of integrating into the educational environment.

In statistical terms, academic adjustment can be quantified through scores that measure these adaptive characteristics. For example, students might be asked about their study habits, time management skills, and how confidently they tackle academic challenges. These scores are then used as predictor variables in regression models to understand their impact on outcomes like GPA.
  • Scores like these help determine how well each student is performing academically.
  • A higher academic adjustment score usually indicates better performance and coping mechanisms in an academic setting.
In our regression model, this score is represented by the variable \(x_1\) which contributes to predicting the student's current GPA independently of other factors.
Race Variable
In multivariate analyses, such as multiple regression, it is common to include demographic variables to account for possible differences in academic outcomes. In this context, the race variable is included to examine if and how race affects students' GPAs.

In the provided exercise, the race variable is coded as a binary variable, where "white" students are assigned a value of 0, and "other" races are given a value of 1. This coding allows researchers to understand how being part of a racial minority could impact academic success.
  • This binary coding simplifies the variable, allowing for direct comparison between the two groups.
  • The analysis focuses on whether the race variable has a significant independent contribution to predicting the GPA, alongside other variables.
In the regression model, the race variable \(x_2\) interacts independently, meaning it directly influences the GPA without being influenced by or altering the effects of other variables like academic adjustment. This is crucial for understanding any racial disparities in educational outcomes.
Independent Contributions
In the context of the regression analysis described in the exercise, independent contributions refer to the way each variable (academic adjustment and race) affects the dependent variable (GPA) separately. They do not modify each other's impact on the outcome.

This means each independent variable adds unique information or predictive power to the model, which helps in understanding the different factors contributing to GPA. In simpler terms, the model is structured to separate the unique effect of academic adjustment from that of the race variable, without them influencing each other.
  • Each variable's coefficient in the regression model reflects its independent effect on GPA.
  • This setup helps identify the specific impact of academic adjustment and race on GPA, facilitating targeted interventions where necessary.
The absence of an interaction term in the regression model confirms that the variables contribute independently. This is based on the problem statement stating no interaction, which aligns with the goal of understanding each factor's unique influence on academic achievement.

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Most popular questions from this chapter

The article "Impacts of On-Campus and Off-Campus Work on First-Year Cognitive Outcomes" (Journal of College Student Development \([1994]: 364-370\) ) reported on a study in which \(y=\) spring math comprehension score was regressed against \(x_{1}=\) previous fall test score, \(x_{2}=\) previous fall academic motivation, \(x_{3}=\) age, \(x_{4}=\) number of credit hours, \(x_{5}=\) residence \((1\) if on campus, 0 otherwise), \(x_{6}=\) hours worked on campus, and \(x_{7}=\) hours worked off campus. The sample size was \(n=210\), and \(R^{2}=.543\). Test to see whether there is a useful linear relationship between \(y\) and at least one of the predictors.

Obtain as much information as you can about the \(P\) -value for the \(F\) test for model utility in each of the following situations: a. \(k=2, n=21\), calculated \(F=2.47\) b. \(k=8, n=25\), calculated \(F=5.98\) c. \(k=5, n=26\), calculated \(F=3.00\) d. The full quadratic model based on \(x_{1}\) and \(x_{2}\) is fit, \(n=20\), and calculated \(F=8.25\). \mathrm{\\{} e . ~ \(k=5, n=100\), calculated \(F=2.33\)

This exercise requires the use of a computer package. The cotton aphid poses a threat to cotton crops in Iraq. The accompanying data on \(y=\) infestation rate (aphids/100 leaves) \(x_{1}=\) mean temperature \(\left({ }^{\circ} \mathrm{C}\right)\) \(x_{2}=\) mean relative humidity appeared in the article "Estimation of the Economic Threshold of Infestation for Cotton Aphid" (Mesopotamia Journal of Agriculture [1982]: 71-75). Use the data to find the estimated regression equation and assess the utility of the multiple regression model $$ y=\alpha+\beta_{1} x_{1}+\beta_{2} x_{2}+e $$ $$ \begin{array}{rrrrrr} \boldsymbol{y} & \boldsymbol{x}_{1} & \boldsymbol{x}_{2} & \boldsymbol{y} & \boldsymbol{x}_{1} & \boldsymbol{x}_{2} \\ \hline 61 & 21.0 & 57.0 & 77 & 24.8 & 48.0 \\ 87 & 28.3 & 41.5 & 93 & 26.0 & 56.0 \\ 98 & 27.5 & 58.0 & 100 & 27.1 & 31.0 \\ 104 & 26.8 & 36.5 & 118 & 29.0 & 41.0 \\ 102 & 28.3 & 40.0 & 74 & 34.0 & 25.0 \\ 63 & 30.5 & 34.0 & 43 & 28.3 & 13.0 \\ 27 & 30.8 & 37.0 & 19 & 31.0 & 19.0\\\ 14 & 33.6 & 20.0 & 23 & 31.8 & 17.0 \\ 30 & 31.3 & 21.0 & 25 & 33.5 & 18.5 \\ 67 & 33.0 & 24.5 & 40 & 34.5 & 16.0 \\ 6 & 34.3 & 6.0 & 21 & 34.3 & 26.0 \\ 18 & 33.0 & 21.0 & 23 & 26.5 & 26.0 \\ 42 & 32.0 & 28.0 & 56 & 27.3 & 24.5 \\ 60 & 27.8 & 39.0 & 59 & 25.8 & 29.0 \\ 82 & 25.0 & 41.0 & 89 & 18.5 & 53.5 \\ 77 & 26.0 & 51.0 & 102 & 19.0 & 48.0 \\ 108 & 18.0 & 70.0 & 97 & 16.3 & 79.5 \end{array} $$

This exercise requires the use of a computer package. The accompanying data resulted from a study of the relationship between \(y=\) brightness of finished paper and the independent variables \(x_{1}=\) hydrogen peroxide (\% by weight), \(x_{2}=\) sodium hydroxide (\% by weight), \(x_{3}=\) silicate \((\%\) by weight \()\), and \(x_{4}=\) process temperature ("Advantages of CE-HDP Bleaching for High Brightness Kraft Pulp Production," TAPPI [1964]: 107A-173A). $$ \begin{array}{ccccc} x_{1} & x_{2} & x_{3} & x_{4} & y \\ \hline .2 & .2 & 1.5 & 145 & 83.9 \\ .4 & .2 & 1.5 & 145 & 84.9 \\ .2 & .4 & 1.5 & 145 & 83.4 \\ .4 & .4 & 1.5 & 145 & 84.2 \\ .2 & .2 & 3.5 & 145 & 83.8 \\ .4 & .2 & 3.5 & 145 & 84.7 \\ .2 & .4 & 3.5 & 145 & 84.0 \\ .4 & .4 & 3.5 & 145 & 84.8 \\ .2 & .2 & 1.5 & 175 & 84.5 \\ .4 & .2 & 1.5 & 175 & 86.0 \\ .2 & .4 & 1.5 & 175 & 82.6 \\ .4 & .4 & 1.5 & 175 & 85.1 \\ .2 & .2 & 3.5 & 175 & 84.5 \\ .4 & .2 & 3.5 & 175 & 86.0 \\ .2 & .4 & 3.5 & 175 & 84.0 \\ .4 & .4 & 3.5 & 175 & 85.4 \\ .1 & .3 & 2.5 & 160 & 82.9 \\ .5 & .3 & 2.5 & 160 & 85.5\\\ .3 & .1 & 2.5 & 160 & 85.2 \\ .3 & .5 & 2.5 & 160 & 84.5 \\ .3 & .3 & 0.5 & 160 & 84.7 \\ .3 & .3 & 4.5 & 160 & 85.0 \\ .3 & .3 & 2.5 & 130 & 84.9 \\ .3 & .3 & 2.5 & 190 & 84.0 \\ .3 & .3 & 2.5 & 160 & 84.5 \\ .3 & .3 & 2.5 & 160 & 84.7 \\ .3 & .3 & 2.5 & 160 & 84.6 \\ .3 & .3 & 2.5 & 160 & 84.9 \\ .3 & .3 & 2.5 & 160 & 84.9 \\ .3 & .3 & 2.5 & 160 & 84.5 \\ .3 & .3 & 2.5 & 160 & 84.6 \end{array} $$ a. Find the estimated regression equation for the model that includes all independent variables, all quadratic terms, and all interaction terms. b. Using a \(.05\) significance level, perform the model utility test. c. Interpret the values of the following quantities: SSResid, \(R^{2}, s_{e}\)

For the multiple regression model in Exercise \(14.4\), the value of \(R^{2}\) was \(.06\) and the adjusted \(R^{2}\) was \(.06 .\) The model was based on a data set with 1136 observations. Perform a model utility test for this regression.

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