## 统计代写|生物统计代写Biostatistics代考|Simple Random Sampling

The first sampling plan that will be discussed is the simple random sample. A simple random sample of size $n$ is a sample consisting of $n$ sampling units selected in a fashion that every possible sample of $n$ units has the same chance of being selected. In a simple random sample, every possible sample has the same chance of being selected, and moreover, each sampling unit has the same chance of being drawn in a sample. Simple random sampling is a reasonable sampling plan for sampling homogeneous or heterogeneous populations that do not have distinct subpopulations that are of interest to the researcher.
Example 3.3
Simple random sampling might be a reasonable sampling plan in the following scenarios:
a. A pharmaceutical company is checking the quality control issues of the tablet form of a new drug. Here, the company might take a random sample of tablets from a large pool of available drug tablets it has recently manufactured.
b. The Federal Food and Drug Administration (FDA) may take a simple random sample of a particular food product to check the validity of the information on the nutrition label.
c. A state might wish to take a simple random sample of medical doctors to review whether or not the state’s continuing education requirements are being satisfied.
d. A tederal or state environment agency may wish to take a simple random sample of homes in a mining town to investigate the general health of the town’s inhabitants and contamination problems in the homes resulting from the mining operation.

The number of possible simple random samples of size $n$ selected from a sampling frame listing of $N$ sampling units is
$$\left(\begin{array}{l} N \ n \end{array}\right)=\frac{N !}{n !(N-n) !}$$
The probability that any one of the possible simple random samples of $n$ units selected from a sampling frame of $N$ units is
$$\frac{1}{\frac{N !}{n !(N-n) !}}=\frac{n !(N-n) !}{N !}$$
In most research studies, the number of units in the target population is fairly large, and therefore, the number of possible simple random samples will also be extremely large. For example, suppose the sampling frame has $N=100$ sampling units and a simple random sample of $n=10$ units will be selected.

## 统计代写|生物统计代写Biostatistics代考|Stratified Random Sampling

When a target population has well-defined subpopulations, the research questions are usually focused on the parameters of the subpopulations. In this case, it is important that the random sample contains sufficient data for estimating the parameters of interest in the subpopulations. Because a simple random sample cannot guarantee that each subpopulation is sufficiently represented in a sample, simple random sampling is generally not the most efficient method of sampling a target population with well-defined subpopulations.

A random sampling plan that is designed specifically for populations having distinct subpopulations is stratified random sampling. A stratified random sample should be used when the target population has well-defined and nonoverlapping subpopulations. The subpopulations of the target population are referred to as strata and a single subpopulation is called a stratum. A stratified random sample is a sample that is drawn by collecting a simple random sample from each stratum in the population. The process for drawing a stratified random sample is outlined below.

Having good sampling frames for each strata and determining the appropriate sample sizes for each strata are critical components of a well-designed stratified random sampling plan. The cost of sampling within the strata and the variability within each stratum play important roles in the determination of the overall sample size and the strata sample sizes. Determination of the appropriate sample size for a stratified random sample and allocation of the sample to the strata will be discussed in detail in Section 3.3.

In biomedical research studies, target populations having subpopulations are the norm rather than the exception. For example, studies involving humans often have subpopulations due to gender, race, blood type, and many other human characteristics. To investigate how these subpopulations of humans differ in a biomedical research problem, a stratified random sample can often be used to obtain the sample data that will be used in comparing the subpopulations of interest.

# 生物统计代考

## 统计代写|生物统计代写Biostatistics代考|Simple Random Sampling

：一家制药公司正在检查一种新药片剂的质量控制问题。在这里，该公司可能会从其最近生产的大量可用药片中随机抽取片剂样本。

C。一个州可能希望对医生进行简单的随机抽样，以审查该州的继续教育要求是否得到满足。
d。联邦或州环境机构可能希望对采矿城镇的房屋进行简单的随机抽样，以调查该镇居民的总体健康状况以及采矿作业导致的房屋污染问题。

(ñ n)=ñ!n!(ñ−n)!

1ñ!n!(ñ−n)!=n!(ñ−n)!ñ!

## 统计代写|生物统计代写Biostatistics代考|Stratified Random Sampling

myassignments-help数学代考价格说明

1、客户需提供物理代考的网址，相关账户，以及课程名称，Textbook等相关资料~客服会根据作业数量和持续时间给您定价~使收费透明，让您清楚的知道您的钱花在什么地方。

2、数学代写一般每篇报价约为600—1000rmb，费用根据持续时间、周作业量、成绩要求有所浮动(持续时间越长约便宜、周作业量越多约贵、成绩要求越高越贵)，报价后价格觉得合适，可以先付一周的款，我们帮你试做，满意后再继续，遇到Fail全额退款。

3、myassignments-help公司所有MATH作业代写服务支持付半款，全款，周付款，周付款一方面方便大家查阅自己的分数，一方面也方便大家资金周转，注意:每周固定周一时先预付下周的定金，不付定金不予继续做。物理代写一次性付清打9.5折。

Math作业代写、数学代写常见问题

myassignments-help擅长领域包含但不是全部: