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For which of the following combinations of sample size and population proportion would the standard deviation of \(\hat{p}\) be smallest? $$ \begin{array}{ll} n=40 & p=0.3 \\ n=60 & p=0.4 \\ n=100 & p=0.5 \end{array} $$

Short Answer

Expert verified
The smallest standard deviation of \(\hat{p}\) is \(\approx 0.05\), which corresponds to the combination with \(n=100\) and \(p=0.5\).

Step by step solution

01

Calculate the standard deviation of \(\hat{p}\) for each combination

Using the formula above, we can find the standard deviation of \(\hat{p}\) for each combination as follows: 1. For \(n=40\) and \(p=0.3\): $$ \sigma_{\hat{p}} = \sqrt{\frac{0.3 (1-0.3)}{40}} \approx 0.073 $$ 2. For \(n=60\) and \(p=0.4\): $$ \sigma_{\hat{p}} = \sqrt{\frac{0.4 (1-0.4)}{60}} \approx 0.063 $$ 3. For \(n=100\) and \(p=0.5\): $$ \sigma_{\hat{p}} = \sqrt{\frac{0.5 (1-0.5)}{100}} \approx 0.05 $$
02

Compare the standard deviations to find the smallest value

We have calculated the standard deviation of \(\hat{p}\) for all three combinations: 1. For \(n=40\) and \(p=0.3\), \(\sigma_{\hat{p}} \approx 0.073\) 2. For \(n=60\) and \(p=0.4\), \(\sigma_{\hat{p}} \approx 0.063\) 3. For \(n=100\) and \(p=0.5\), \(\sigma_{\hat{p}} \approx 0.05\) We can see that the smallest standard deviation of \(\hat{p}\) is \(\approx 0.05\), which corresponds to the combination with \(n=100\) and \(p=0.5\).

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Key Concepts

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

Standard Deviation
Understanding the concept of standard deviation is crucial for interpreting data and statistics. In the context of a sample proportion like \( \hat{p} \) from a binomial distribution, the standard deviation gives us insight into how much variation we can expect from the true population proportion. Essentially, it tells us how tightly the sample proportions are clustered around the true population proportion. The formula for the standard deviation of the sample proportion is given by \( \sigma_{\hat{p}} = \sqrt{\frac{p(1-p)}{n}} \), where \( p \) is the population proportion and \( n \) is the sample size. A smaller standard deviation means the sample proportions are more closely packed around the population proportion, indicating more precise estimates.
Sample Size
Sample size, denoted as \( n \), plays a pivotal role in the reliability of statistical calculations. The size of the sample influences the standard deviation of a sample proportion. As per the formula \( \sigma_{\hat{p}} = \sqrt{\frac{p(1-p)}{n}} \), increasing \( n \) results in a smaller standard deviation, which suggests a more precise estimate of the population proportion. This is because a larger sample size tends to reduce the impact of random fluctuations and provide a better approximation of the population parameter. When designing an experiment or survey, it is essential to choose a proper sample size to balance the tradeoff between cost and precision.
Population Proportion
The population proportion, symbolized by \( p \) in statistical formulas, is a measure that represents the fraction of members in a population who have a particular attribute. When conducting surveys or experiments, the population proportion is often what researchers are trying to estimate. It is a crucial component in calculating the standard deviation of the sample proportion. The value of \( p \) can vary between 0 and 1, and both extremes of this range (very low or very high proportions) can result in a lower standard deviation for \( \hat{p} \). However, when exactly \( p = 0.5 \) the standard deviation of the sample proportion reaches its maximum, taking into account a fixed sample size.
Statistics Calculations
Statistics calculations involve taking the theories and formulas of statistics and applying them to real-world data. The computations can include various measures of central tendency, dispersion, correlation, and inferential statistics, among others. In this particular scenario, we applied the formula for the standard deviation of the sample proportion to different combinations of sample size and population proportion. The step-by-step solution provides a practical application of statistical theory, helping students connect the abstract formulas to tangible outcomes. When comparing the standard deviations across different sample sizes and population proportions, we could determine which combination yields the most precise estimation (the smallest standard deviation), which was for the sample size \( n = 100 \) and population proportion \( p = 0.5 \) in our exercise. This exemplifies the use of calculations to inform decisions in statistical research and practice.

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Most popular questions from this chapter

The report "A Crisis in Civic Education" (January 2016, goacta.org/images/download/A_Crisis_in_Civic_Education .pdf, retrieved May 3,2017 ) indicated that in a survey of a random sample of 1000 recent college graduates, 96 indicated that they believed that Judith Sheindlin (also known on TV as "Judge Judy") was a member of the U.S. Supreme Court. Is it reasonable to conclude that the proportion of recent college graduates who have this incorrect belief is greater than 0.09 \((9 \%) ?\) (Hint: Use what you know about the sampling distribution of \(\hat{p}\). You might also refer to Example \(8.5 .)\)

Consider the two relative frequency histograms at the top of the next page. The histogram on the left was constructed by selecting 100 different random samples of size 40 from a population consisting of \(20 \%\) part-time students and \(80 \%\) full-time students. For each sample, the sample proportion of part-time students, \(\hat{p},\) was calculated. The \(100 \hat{p}\) values were used to construct the histogram. The histogram on the right was constructed in a similar way, but using samples of size 70 . a. Which of the two histograms indicates that the value of \(\hat{p}\) has smaller sample-to-sample variability? How can you tell? b. For which of the two sample sizes, \(n=40\) or \(n=70,\) do you think the value of \(\hat{p}\) would be less likely to be close to \(0.20 ?\) What about the given histograms supports your choice?

The article "The Average American Is in Credit Card Debt, No Matter the Economy" (Money Magazine, February 9, 2016) reported that only \(35 \%\) of credit card users pay off their bill every month. Suppose that the reported percentage was based on a random sample of 1000 credit card users. Suppose you are interested in learning about the value of \(p,\) the proportion of all credit card users who pay off their bill every month. The following table is similar to the table that appears in Examples 8.4 and \(8.5,\) and is meant to summarize what you know about the sampling distribution of \(\hat{p}\) in the situation just described. The "What You Know" information has been provided. Complete the table by filling in the "How You Know It" column.

Consider the following statement: Fifty people were selected at random from those attending a football game. The proportion of these 50 who made a food or beverage purchase while at the game was 0.83 . a. Is the number that appears in boldface in this statement a sample proportion or a population proportion? b. Which of the following use of notation is correct, \(p=0.83\) or \(\hat{p}=0.83 ?\)

Consider the following statement: The Department of Motor Vehicles reports that the proportion of all vehicles registered in California that are imports is \(0.22 .\) a. Is the number that appears in boldface in this statement a sample proportion or a population proportion? b. Which of the following use of notation is correct, \(p=0.22\) or \(\hat{p}=0.22 ?\) (Hint: See definitions and notation on page \(403 .\) )

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