### 统计代写|回归分析作业代写Regression Analysis代考|STAT2220

statistics-lab™ 为您的留学生涯保驾护航 在代写回归分析Regression Analysis方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写回归分析Regression Analysis代写方面经验极为丰富，各种代写回归分析Regression Analysis相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 统计代写|回归分析作业代写Regression Analysis代考|Evaluating the Linearity Assumption Using Graphical Methods

While we are not big fans of data analysis “recipes,” in regression or elsewhere, which instruct you to perform step 1, step 2, step 3, etc. for the analysis of your data, we are happy to recommend the following first step for the analysis of regression data.
Step 1 of any analysis of regression data
Plot the ordinary $\left(x_i, y_i\right)$ scatterplot, or scatterplots if there are multiple $X$ variables.
The simple $\left(x_i, y_i\right)$ scatterplot gives you immediate insight into the viability of the linearity, constant variance, and normality assumptions (see Section $1.8$ for examples of such scatterplots). It will also alert you to the presence of outliers.

To evaluate linearity using the $\left(x_i, y_i\right)$ scatterplot, simply look for evidence of curvature. You can overlay the LOESS fit to better estimate the form of the curvature. Recall, though, that all assumptions refer to the data-generating process. Thus, if you are going to claim there is curvature, such curvature should make sense in the context of the subject matter. For one example, boundary constraints can force curvature: If the minimum $Y$ is zero, then the curve must flatten for $X$ values where $Y$ is close to zero. For another example, in the case of the product preference vs. product complexity shown in Figure 1.16, there is a subject matter rationale for the curvature: People prefer more complexity up to a point, after which more complexity is less desirable. Ideally, you should be able to justify curvature in terms of the processes that produced your data.

A refinement of the $\left(x_i, y_i\right)$ scatterplot is the residual $\left(x_i, e_i\right)$ scatterplot. This scatterplot is an alternative, “magnified” view of the $\left(x_i, y_i\right)$ scatterplot, where the $e=0$ horizontal line in the $\left(x_i, e_i\right)$ scatterplot corresponds to the least-squares line in the $\left(x_i, y_i\right)$ scatterplot. Look for upward or downward ” $\mathrm{U}^{\prime \prime}$ shape to suggest curvature; overlay the LOESS fit to the $\left(x_i, e_i\right)$ data to help see these patterns.

You can also use the $\left(\hat{y}i, e_i\right)$ scatterplot to check the linearity assumption. In simple regression (i.e., one $X$ variable), the $\left(\hat{y}_i, e_i\right)$ scatterplot is identical to the $\left(x_i, e_i\right)$ scatterplot, with the exception that the horizontal scale is linearly transformed via $\hat{y}_i=\hat{\beta}_0+\hat{\beta}_1 x_i$. When the estimated slope is negative, the horizontal axis is “reflected”-large values of $x$ map to small values of $\hat{y}_i$ and vice versa. You can use this plot just like the $\left(x_i, e_i\right)$ scatterplot. In simple regression, the $\left(\hat{y}_i, e_i\right)$ scatterplot offers no advantage over the $\left(x_i, e_i\right)$ scatterplot. However, in multiple regression, the $\left(\hat{y}_i, e_i\right)$ scatterplot is invaluable as a quick look at the overall model, since there is just one $\left(\hat{y}_i, e_i\right)$ plot to look at, instead of several $\left(x{i j}, e_i\right)$ plots (one for each $X_j$ variable). This $\left(\hat{y}_i, e_i\right)$ scatterplot, which you can call a “predicted/residual scatterplot,” is automatically provided by $\mathrm{R}$ when you plot a fitted lm object.

## 统计代写|回归分析作业代写Regression Analysis代考|Evaluating the Linearity Assumption Using Hypothesis Testing Methods

Here, we will get slightly ahead of the flow of the book, because multiple regression is covered in the next chapter. A simple, powerful way to test for curvature is to use a multiple regression model that includes a quadratic term. The quadratic regression model is given by:
$$Y=\beta_0+\beta_1 X+\beta_2 X^2+\varepsilon$$
This model assumes that, if there is curvature, then it takes a quadratic form. Logic for making this assumption is given by “Taylor’s Theorem,” which states that many types of curved functions are well approximated by quadratic functions.

Testing methods require restricted (null) and unrestricted (alternative) models. Here, the null model enforces the restriction that $\beta_2=0$; thus the null model states that the mean response is a linear (not curved) function of $x$. So-called “insignificance” (determined historically by $p>0.05$ ) of the estimate of $\beta_2$ means that the evidence of curvature in the observed data, as indicated by a non-zero estimate of $\beta_2$ or by a curved LOESS fit, is explainable by chance alone under the linear model. “Significance” (determined historically by $p<0.05$ ) means that such evidence of curvature is not easily explained by chance alone under the linear model.

But you should not take the result of this $p$-value based test as a “recipe” for model construction. If “significant,” you should not automatically assume a curved model. Instead, you should ask, “Is the curvature dramatic enough to warrant the additional modeling complexity?” and “Do the predictions differ much, whether you use a model for curvature or the ordinary linear model?” If the answers to those questions are “No,” then you should use the linear model anyway, even if it was “rejected” by the $p$-value based test.

In addition, models employing curvature (particularly quadratics) are notoriously poor at the extremes of the $x$-range(s). So again, you can easily prefer the linear model, even if the curvature is “significant” $(p<0.05)$.

Conversely, if the quadratic term is “insignificant,” it does not mean that the function is linear. Recall from Chapter 1 that the linearity is usually false, a priori; hence, “insignificance” means that you have failed to detect curvature. If the test for the quadratic term is “insignificant,” it is most likely a Type II error.

Even when the curvature does not have a perfectly quadratic form, the quadratic test is usually very powerful; rare exceptions include cases where the curvature is somewhat exotic. If the quadratic model is grossly wrong for modeling curvature in your application, then you should use a test based on a model other than the quadratic model.

## 统计代写|回归分析作业代写Regression Analysis代考|Evaluating the Linearity Assumption Using Hypothesis Testing Methods

$$Y=\beta_0+\beta_1 X+\beta_2 X^2+\varepsilon$$

## 广义线性模型代考

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。