A variable is said to be uniformly distributed or to have a uniform distribution with parameters \(a\) and \(b\) if its distribution has the shape of the horizontal line segment with equation \(y=\frac{1}{(b-a)}\) for \(a<x<b\). The mean and standard deviation of such a variable are \(\frac{(a+b)}{2}\) and \(\frac{(b-a)}{\sqrt{12}}\) respectively. The basic random number generator on a computer or calculator which returns a number between \(0\) and \(1\), simulates a variable having a uniform distribution with parameters \(0\) and \(1\).

a. Sketch the distribution of a uniformly distributed variable with parameters \(0\) and \(1\). Observe from your sketch that such a variable is far from being normally distributed.

b. Use the technology of your choice to simulate \(2000\) samples of two random numbers between \(0\) and \(1\).

c. Find the sample mean of each of the \(2000\) samples obtained in part (b).

d. Determine the mean and standard deviation of the \(2000\) sample means.

e. Theoretically what are the mean and the standard deviation of all possible sample means for samples of size \(2\)? Compare your answers to those you obtained in part (d).

f. Obtained a histogram of the \(2000\) sample means. Is the histogram bell shaped? Would you expect it to be?

g. Repeat parts (b)-(f) for a sample size of \(35\).

Short Answer

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Part a.

Part b. The samples will be like

Part c. The mean will be \(\mu =[49.3615, 49.1953, 48.7853,49.1773]\)

Part d. The standard deviation and mean will be

\(\mu_{\bar{x}}=49.6020\)

\(\sigma_{\bar{x}}=\frac{10.14}{\sqrt{4}}=5.07\)

Part e. \(\mu_{\bar{x}}=49.34\)

\(\sigma_{\bar{x}}=\frac{10.14}{\sqrt{4}}=5.07\)

Part f.

Step by step solution

01

Part a. Step 1. Given information

The value of variable is

\(a=0\)

\(b=1\)

\(n=2\)

02

Part a. Step 2. Calculation

Calculate the mean and standard deviation using given relation

\(mean=\frac{a+b}{2}=0.5\)

\(\sigma=\frac{(b-a)}{\sqrt{12}}=0.2887\)

The compute the value of the function

\(y=\frac{1}{b-a}=1\)

So, we can see that the function value is 1 then sketch a graph using MATLAB.

Program:

Query:

  • First, we have defined given variables.
  • Then calculate the mean and standard deviation.
  • Then calculate the value of the function.
  • Sketch a graph.
03

Part b. Step 1. Calculation

So, according to the question I have used MATLAB to generate the samples.

We use the function \(“norminv (rand (1000,4), 49.34, 10.14)”\).

After using the above function in MATLAB, we will get the \(1000\) sample for \(4\) dancers.

Program:

Query:

  • First, we have defined the number of samples.
  • Then using function “norminv” to find out the samples for dancers.
04

Part c. Step 1. Calculation

So, according to the question I have used MATLAB to generate the samples.

We use the function \(“norminv (rand (1000,4), 49.34, 10.14)”\).

Then calculate the mean

\(\mu=\frac{\sum_{i-1}^{1000}x_{i}}{n}\)

After solving the equation, we will get

\(\mu =[49.3615, 49.1953, 48.7853,49.1773]\)

Program:

Query:

  • First, we have defined the number of samples.
  • Then using function “norminv” to find out the samples for dancers.
  • Then calculate the mean using function “mean”.
05

Part d. Step 1. Calculation

So, according to the question I have used MATLAB to generate the samples.

We use the function \(“norminv (rand (1000,4), 49.34, 10.14)”\).

Then calculate the mean

\(\mu=\frac{\sum_{i-1}^{1000}x_{i}}{n}\)

After solving the equation, we will get

\(\mu =[49.3615, 49.1953, 48.7853,49.1773]\)

Calculate the mean of means

\(\mu_{\bar{x}}=\bar{\mu}\)

and standard deviation

\(\sigma_{\bar{x}}=\frac{10.14}{\sqrt{4}}=5.07\)

Program:

Query:

  • First, we have defined the number of samples.
  • Then using function “norminv” to find out the samples for dancers.
  • Then calculate the mean using function “mean”.
  • Calculate the mean of means and standard deviation.
06

Part e. Step 1. Calculation

The mean of the sampling distribution is equal to the population mean.

\(\mu_{\bar{x}}=\mu=49.34\)

The standard deviation of the sampling distribution is equal to the population standard deviation divide by the square root of the sample size.

\(\sigma_{\bar{x}}=\frac{10.14}{\sqrt{4}}=5.07\)

07

Part f. Step 1. 

So, according to the question I have used MATLAB to generate the samples.

We use the function \(“norminv (rand (1000,4), 49.34, 10.14)”\).

Then calculate the mean

\(\mu=\frac{\sum_{i-1}^{1000}x_{i}}{n}\)

After solving the equation, we will get

\(\mu =[49.3615, 49.1953, 48.7853,49.1773]\)

Calculate the mean of means

\(\mu_{\bar{x}}=\bar{\mu}\)

\(\mu_{\bar{x}}=49.6020\)

and standard deviation

\(\sigma_{\bar{x}}=\frac{10.14}{\sqrt{4}}=5.07\)

Program:

Query:

  • First, we have defined the number of samples.
  • Then using function “norminv” to find out the samples for dancers.
  • Then calculate the mean using function “mean”.
  • Calculate the mean of means and standard deviation.
  • Then sketch a histogram of the samples.

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Most popular questions from this chapter

7.54 Unbiased and Biased Estimators. A statistic is said to be an unbiased estimator of a parameter if the mean of all its possible values equals the parameter. otherwise, it is said to be a biased estimator. An unbiased estimator yields, on average, the correct value of the parameter, whereas a biased estimator does not.
a. Is the sample mean an unbiased estimator of the population mean? Explain your answer.
b. Is the sample median an unbiased estimator of the population median? (Hint: Refer to Example 7.2 on pages 292-293. Consider samples of size 2.)

7.46 Young Adults at Risk. Research by R. Pyhala et al. shows that young adults who were born prematurely with very low birth weights (below 1500grams) have higher blood pressure than those born at term. The study can be found in the article. "Blood Pressure Responses to Physiological Stress in Young Adults with Very Low Birth Weight" (Pediatrics, Vol. 123, No, 2, pp. 731-734). The researchers found that systolic blood pressures, of young adults who were born prematurely with very low birth weights have mean 120.7mmHgand standard deviation 13.8mmHg.
a. Identify the population and variable.
b. For samples of 30 young adults who were born prematurely with very low birth weights, find the mean and standard deviation of all possible sample mean systolic blood pressures. Interpret your results in words.
c. Repeat part (b) for samples of size 90 .

Each years, Forbers magazine publishes a list of the richest people in the United States. As of September 16, 2013,the six richest Americans and their wealth (to the nearest billion dollars) are as shown in the following table. Consider these six people a population of interest.

Part (a): Calculate the mean wealth, μ, of the six people.

Part (b): For samples of size 2, construct a table similar to Table 7.2 on page 293. (There are 15 possible samples of size 2.)

Part (c): Draw a dotplot for the sampling distribution of the sample mean for samples of size 2.

Part (d): For a random sample of size2, what is the chance that the sample mean will equal the population mean?

Part (e): For a random sample of size 2, determine the probability that the mean wealth of the two people obtained will be within 3 of the population mean. Interpret your result in terms of percentages.

New York City 10-kmRun. As reported by Rumле's World magazine, the times of the finishers in the New York City 10-km run are normally distributed with a mean of 61 minutes and a standard deviation of 9minutes. Do the following for the variable "finishing time61min of finishers in the New York City 10-kmrun.

a. Find the sampling distribution of the sample mean for samples of size 4

b. Repeat part (a) for samples of size 9

C. Construct graphs similar to those shown in Fig.7.4on-page 304

d. Obtain the percentage of all samples of four finishers that have mean finishing times within 5minutes of the population mean finishing time of 61 minutes. Interpret your answer in terms of sampling error.

e. Repeat part (d) for samples of size 9

Relative to the population mean, what happens to the possible sample means for samples of the same size as the sample size increases? Explain the relevance of this property in estimating a population means by a sample mean.

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