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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 of the sample proportion is 0.007. The sampling distribution of \(\hat{p}\) is not approximately normal in this case because \(n \cdot P < 5\). The smallest value of \(n\) that makes the sampling distribution of \(\hat{p}\) approximately normal is \(n = 1000\).

Step by step solution

01

Find the mean value of the sample proportion

Start by using the formula for the mean of the sample proportion which is the probability of the event. The given problem states that the chromosome defect occurs in 1 in 200 adult Caucasian males. So, the probability \(P\) that a randomly selected adult Caucasian male will have the chromosome defect is \(P = 1/200 = 0.005\). Therefore, \(\mu_{p} = P = 0.005\).
02

Compute the standard deviation of the sample proportion

Next, use the formula for the standard deviation of the sample proportion, \( \sigma_{p} = \sqrt{ \frac{P \cdot (1 - P)}{n}} \). Substitute \(P = 0.005\) and \(n = 100\) to get \(\sigma_{p} = \sqrt{ \frac{0.005 \cdot (1 - 0.005)}{100}} = 0.007\).
03

Determine if it follows an approximate normal distribution

Apply the Rule of Thumb for the central limit theorem which states that if the sample size is large enough, the distribution of the sample proportion will be approximately normal, regardless of the shape of the population distribution. According to this rule, the distribution of the sample proportion will be approximately normal if both \(n \cdot P \geq 5 \) and \(n \cdot (1 - P) \geq 5\) hold true. Substitute \(P = 0.005\) and \(n = 100\) to get \(n \cdot P = 100 \cdot 0.005 = 0.5\) and \(n \cdot (1 - P) = 100 \cdot (1 - 0.005) = 99.5\). While \(n \cdot (1 - P) \geq 5\) is true, \(n \cdot P \geq 5 \) is not, hence the distribution is not approximately normal.
04

Find the smallest value of \(n\)

To find the smallest value of \(n\), both conditions of the rule \(n \cdot P \geq 5 \) and \(n \cdot (1 - P) \geq 5\) must be true. If we consider \(n \cdot P \geq 5 \), we can solve for \(n\) by dividing both sides by \(P\). Thus, \(n \geq \frac{5}{P} = \frac{5}{0.005} = 1000\). So, the smallest value of \(n\) that makes the sampling distribution of \(\hat{p}\) approximately normal is \(n = 1000\).

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