### 统计代写|实验设计作业代写experimental design代考|THE EXPERIMENTAL DESIGN MODEL

statistics-lab™ 为您的留学生涯保驾护航 在代写实验设计experimental designatistical Modelling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。我们的专家在代写实验设计experimental design代写方面经验极为丰富，各种代写实验设计experimental design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|实验设计作业代写experimental design代考|THE EXPERIMENTAL DESIGN MODEL

Back in Chapter 1, Section 1, it was explained that the aim of all the work so far is to fit models to a population using data from a sample. The model so fitted shows what values of $y$ are 1 kely to be associated with any given values of the $x$ ‘s. Just as any elementary statistics text will warn that a correlation does not imply causation, so a well fltting regression model does not imply that changes in the $x$ values will cause changes in the y variable in’ accordance the with model. If the model has been constructed by passive observation of sets of $y^{\prime} s$ and $x^{\prime} s$, any intervention to change the $x$ values to values which do not occur naturally will change the population to be something different from what the model describes, and so the model no longer applies.
In an experiment a population is not passively observed, but the $x$ values are the result of intervention by the experimenter. The aim then is to intervene to choose $x$ values in such a way as to give accurate estimates of the model parameters with a minimum of effort, and to ensure that the relationships described by the model really do describe the way changes in $y$ are caused by changes in $x$.

## 统计代写|实验设计作业代写experimental design代考|WHAT MAKES AN EXPERIMENT?

One of the 1 argest experiments ever conducted makes an interesting example, partly because it was almost a disaster. The experiment was designed to test the effectiveness of the Salk polio vacoine, and was conducted in the United States in 1954 . A good account of the experiment is in Freedman, Pisani, and Purves, 1978 . There were two difficulties with the experiment. First, polio is a relatively uncommon disease, The vacoine can only be tested if 1 t is tried on a group large enough to contain a reasonable number of polio victims. For the common cold a fer hundred people would be plent y, but for pol1o several hundred thousand were required. Second, polio is a disease which comes and goes from one season to the next. With the common cold, which most people catch most years, if the incidence drops in a test group after administering a vaccine, the drop can probably be attributed to the vacoine. But not so with polio = 1 t may well have been a year in which the disease would have waned anyway.
The original experimental plan for the polio vaccine was to vaccinate second year school children and compare their incidence of polio with that of first and third year children. The intention is clear. The children being compared should be as alike as possible, and this plan would ensure that the geographical area and the time period would be the same for both groups. Of course they would be of different ages, but since the ages of the untreated group brackets that of the treated group one might not expect this to matter too much. A large number of experts must have considered that these remaining differences would not matter because this experiment was put into effect. 221,998 children were vaceinated, 725, 173 here not, and the rate of polio following vaccination was about twice as great $1 n$ the unvaceinated group as in the vaccinated group, $(54$ per 100,000 instead of 25 ).

## 统计代写|实验设计作业代写experimental design代考|Experimental Unit

We will define an experimental unit as that object or group of objects to which a treatment has been randomly assigned. Some examples will make this definftion clear. An educationalist may be comparing teaching methods. Each child is given a test after being taught by the method assigned to $1 \mathrm{t}$, so there is one observation per child. However the child is only an experimental unit if each child were individually assigned to a teaching method. If the children were first divided into small groups, and groups were assigned randomly to teaching method, then the group would become an experimental unft and the observation on it would be the average of all the observations on the individual children. If the two classes were used, each randomly assigned to a teaching method, a class would be an experimental unit, and because there would be no replication, no assessment would be possible. In an experiment comparing weedicides, various combinations of weedicides are randomly assigned to $5 \mathrm{~m} \times 2 \mathrm{~m}$ areas. Within each of these areas $f$ ive $+25 \mathrm{~m} x+25 \mathrm{~m}$ quadrats,

positioned at random, are examined for percent weed cover. This is a very common type of biological experiment, and one where our definition of experimental units is important. The weedicides were assigned to the $5 \mathrm{~m} \times 2 \mathrm{~m}$ areas, and so these are the experimental units, not the $.25 \mathrm{~m} \times .25 \mathrm{~m}$ quadrats.
As a very general and 1 mportant principle, remember that any treatment comparison must be based on one number per experimental unit. This number might often be a mean of several observations, but one must beware of pretending that by increasing the number of subsamples one can increase the replication. It is experimental units which must be replicated.

## 有限元方法代写

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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。