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A certain chromosome defect occurs in only 1 in 200 adult Caucasian males. A random sample of \(n=100\) adult Caucasian males is to be obtained. a. What is the mean value of the sample proportion \(\hat{p}\), and what is the standard deviation of the sample proportion? b. Does \(\hat{p}\) have approximately a normal distribution in this case? Explain. c. What is the smallest value of \(n\) for which the sampling distribution of \(\hat{p}\) is approximately normal?

Short Answer

Expert verified
The mean value of the sample proportion is \(0.005\) and the standard deviation is \(0.0223\). The distribution of the sample proportion \(\hat{p}\) is not normal in this case since both conditions in the Central Limit Theorem are not met. The minimum sample size for the sampling distribution to be approximately normal is \(1000\) males.

Step by step solution

01

Compute Mean Value and Standard Deviation

The mean value of \(\hat{p}\) is equal to \(p\), which is \(0.005\). The standard deviation (\(\sigma\)) of the sampling distribution of \(\hat{p}\) can be calculated using the formula \(\sigma = \sqrt{p(1-p)/n}\), which in this case would be \(\sqrt{0.005 * 0.995/100} = 0.0223\).
02

Evaluate Normality of Sample Proportion

According to the Central Limit Theorem, the distribution of \(\hat{p}\) is approximately normal if both \(np \ge 5\) and \(n(1-p) \ge 5\). In this case, the values are \(100*0.005=0.5\) and \(100*0.995=99.5\), respectively. Therefore, only one condition is satisfied and one is not. So, \(\hat{p}\) does not have a normal distribution in this case.
03

Find Smallest Sample Size for Normality

To find the smallest value of \(n\) for \(\hat{p}\) distribution to be approximately normal, we need both \(np\) and \(n(1-p)\) to be greater than or equal to 5. Solving for \(n\), we obtain \(n \ge 5/p = 5/0.005 = 1000\) males. Therefore, \(n\) should be at least \(1000\).

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Key Concepts

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

Central Limit Theorem
The Central Limit Theorem (CLT) is a fundamental principle in statistics that describes how the distribution of sample means becomes approximately normal as the sample size increases, regardless of the shape of the population distribution. This allows statisticians to make inferences about population parameters even when dealing with non-normal distributions.
In the context of sample proportions, the CLT implies that the distribution of \( \hat{p} \), or the sample proportion, approaches a normal distribution as the sample size (\( n \)) becomes larger. For \( \hat{p} \) to be approximately normal, two conditions must be satisfied: \( np \geq 5 \) and \( n(1-p) \geq 5 \).
  • The first condition ensures that there are enough occurrences of success in the sample.
  • The second condition ensures the presence of sufficient failures, too.
In our example, while the condition \( n(1-p) \geq 5 \) is met, \( np \geq 5 \) is not, so the sample proportion is not normally distributed.
Sampling Distribution
A sampling distribution represents the distribution of a statistic (like the mean or proportion) calculated from numerous samples of a specific size taken from a population. This concept is essential for understanding how sample statistics reflect the actual population parameters.
In this exercise, we focus on the sampling distribution of the sample proportion \( \hat{p} \). The mean of this distribution should equal the true population proportion \( p \), which ensures that the samples reflect the overall population accurately.
The variability or spread of the sampling distribution is given by its standard deviation, calculated as \( \sigma = \sqrt{\frac{p(1-p)}{n}} \). In our scenario, the mean is \( 0.005 \), and the standard deviation is \( 0.0223 \). These values tell us how much the sample proportion \( \hat{p} \) may vary from the true proportion \( p \) in repeated samples.
Sample Proportion
The sample proportion, symbolized as \( \hat{p} \), is a crucial measure in statistics that tells us the ratio of individuals in a sample with a particular characteristic. In simpler terms, it's the fraction of the sample that has a specific trait or attribute, like a genetic defect in our example.
  • It helps estimate the true population proportion \( p \) based on sample data.
  • In our exercise, \( \hat{p} \) is derived from observing chromosome defects in 100 males.
One important factor is that the accuracy and reliability of \( \hat{p} \) improve with larger sample sizes. This is because larger samples tend to better represent the population distribution.
When we calculate the mean value and standard deviation of \( \hat{p} \), we get a better understanding of how well our sample approximates the population proportion. Here, the mean \( \hat{p} \) is the same as the population proportion \( p \), \( 0.005 \), reflecting an accurate point estimate for the proportion of chromosome defects in the population.

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Most popular questions from this chapter

Suppose that a sample of size 100 is to be drawn from a population with standard deviation 10 . a. What is the probability that the sample mean will be within 1 of the value of \(\mu\) ? b. For this example \((n=100, \sigma=10),\) complete each of the following statements by computing the appropriate value: i. Approximately \(95 \%\) of the time, \(\bar{x}\) will be within \(\quad\) of \(\mu\). ii. Approximately \(0.3 \%\) of the time, \(\bar{x}\) will be farther than \(\quad\) from \(\mu\).

A manufacturer of computer printers purchases plastic ink cartridges from a vendor. When a large shipment is received, a random sample of 200 cartridges is selected, and each cartridge is inspected. If the sample proportion of defective cartridges is more than \(.02,\) the entire shipment is returned to the vendor. a. What is the approximate probability that a shipment will be returned if the true proportion of defective cartridges in the shipment is \(.05 ?\) b. What is the approximate probability that a shipment will not be returned if the true proportion of defective cartridges in the shipment is \(.10 ?\)

Consider the following population: \(\\{2,3,3,4,4\\} .\) The value of \(\mu\) is 3.2 , but suppose that this is not known to an investigator, who therefore wants to estimate \(\mu\) from sample data. Three possible statistics for estimating \(\mu\) are Statistic 1: the sample mean, \(\bar{x}\) Statistic 2 : the sample median Statistic 3: the average of the largest and the smallest values in the sample A random sample of size 3 will be selected without replacement. Provided that we disregard the order in which the observations are selected, there are 10 possible samples that might result (writing 3 and \(3^{*}, 4\) and \(4^{*}\) to distinguish the two 3 's and the two 4 's in the population): \(\begin{array}{lllll}2,3,3^{*} & 2,3,4 & 2,3,4^{*} & 2,3^{*}, 4 & 2,3^{*}, 4^{*}\end{array}\) \(2,4,4^{*} \quad 3,3^{*}, 4 \quad 3,3^{*}, 4^{*} \quad 3,4,4^{*} \quad 3^{*}, 4,4^{*}\) For each of these 10 samples, compute Statistics 1,2 , and 3 . Construct the sampling distribution of each of these statistics. Which statistic would you recommend for estimating \(\mu\) and why?

Explain the difference between a population characteristic and a statistic.

The article "Should Pregnant Women Move? Linking Risks for Birth Defects with Proximity to Toxic Waste Sites" (Chance [I992]: \(40-45\) ) reported that in a large study carried out in the state of New York, approximately \(30 \%\) of the study subjects lived within 1 mile of a hazardous waste site. Let \(p\) denote the proportion of all New York residents who live within 1 mile of such a site, and suppose that \(p=.3\). a. Would \(\hat{p}\) based on a random sample of only 10 residents have approximately a normal distribution? Explain why or why not. \(\quad n p=10(0.3)=3<10 .\) b. What are the mean value and standard deviation of \(\hat{p}\) based on a random sample of size \(400 ?\) c. When \(n=400\), what is \(P(.25 \leq \hat{p} \leq .35)\) ? d. Is the probability calculated in Part (c) larger or smaller than would be the case if \(n=500\) ? Answer without actually calculating this probability.

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