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Physicians: Solo Practice A random sample of 328 medical doctors showed that 171 have a solo practice (Source: Practice Patterns of General Internal Medicine, American Medical Association). (a) Let \(p\) represent the proportion of all medical doctors who have a solo practice. Find a point estimate for \(p\). (b) Find a \(95 \%\) confidence interval for \(p\). Give a brief explanation of the meaning of the interval. (c) Interpretation As a news writer, how would you report the survey results regarding the percentage of medical doctors in solo practice? What is the margin of error based on a \(95 \%\) confidence interval?

Short Answer

Expert verified
Point estimate for \(p\) is \(0.521\). \(95\%\) CI: \([0.4671, 0.5749]\). Margin of error: \(5.39\%\).

Step by step solution

01

Identify Given Information

We are given that a random sample of 328 medical doctors is surveyed, out of which 171 have a solo practice. We will use this information to estimate the proportion \( p \) of all doctors having a solo practice.
02

Calculate the Point Estimate for \( p \)

The point estimate for \( p \), the proportion of doctors with a solo practice, is calculated as the ratio of doctors with a solo practice to the total number of doctors in the sample. This is \( \hat{p} = \frac{171}{328} \). Solving this gives \( \hat{p} \approx 0.521 \).
03

Find the Standard Error of \( \hat{p} \)

The standard error (SE) for the sample proportion \( \hat{p} \) is calculated using the formula \[ SE = \sqrt{\frac{\hat{p}(1-\hat{p})}{n}} \] where \( n \) is the sample size. Substitute \( \hat{p} = 0.521 \) and \( n = 328 \): \[ SE = \sqrt{\frac{0.521 \times (1 - 0.521)}{328}} \approx 0.0275 \].
04

Calculate the Margin of Error

For a \(95\%\) confidence interval, we use a Z-score of \(1.96\). The margin of error (MOE) is calculated as: \[ MOE = 1.96 \times SE \approx 1.96 \times 0.0275 \approx 0.0539 \].
05

Construct the Confidence Interval

The \(95\%\) confidence interval is calculated by adding and subtracting the margin of error from the point estimate: \[ CI = \hat{p} \pm MOE \] \[ CI = 0.521 \pm 0.0539 \] This gives the interval \( [0.4671, 0.5749] \).
06

Interpretation of the Confidence Interval

The \(95\%\) confidence interval \([0.4671, 0.5749]\) means that we are \(95\%\) confident the true proportion of all medical doctors with solo practices in the population falls within this interval. This interval indicates that the percentage of doctors with solo practices is likely between \(46.71\%\) and \(57.49\%\).
07

Reporting the Results

As a news writer, you would report that the survey suggests that approximately \(52.1\%\) of medical doctors have a solo practice, with a margin of error of \(5.39\%\) at a \(95\%\) confidence level. This reflects the estimated proportion of doctors in solo practice as between \(46.71\%\) and \(57.49\%\).

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Key Concepts

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

Point Estimate
When tackling statistical problems involving proportions, the "point estimate" is a vital concept. It acts as a best guess or approximation of the true value of a population parameter (like a proportion) based on your sample data. In the context of the exercise, the point estimate for the proportion of medical doctors who have a solo practice is determined by calculating the ratio of doctors in a solo practice to the total number of doctors surveyed. Crystalizing this, the point estimate is calculated as:
  • Number of doctors with solo practices: 171
  • Total number of doctors surveyed: 328
  • Point estimate (\hat{p}\u00a7f): \(61\frac{171}{328} 30\approx\0.521\)
This estimate suggests that about 52.1% of doctors in the sample are in a solo practice. It provides a snapshot of the current pattern seen in your data, giving us a balance between accuracy and simplicity.
Standard Error
The concept of "Standard Error" helps you understand how much variability or "noise" there is in your sample proportion estimate compared to the true population proportion. Think of it as a measure of the reliability of the point estimate. The smaller the standard error, the more reliable the estimate. In the exercise, the standard error for the sample proportion is calculated using the formula:\[ SE = \sqrt{\frac{\hat{p}(1-\hat{p})}{n}} \]Plugging in the values, where \(6c\hat{p}=0.521\) and \(6c n=328\), results in: \[ SE \approx \sqrt{\frac{0.521 \times (1-0.521)}{328}} \approx 0.0275 \]This calculation indicates that the point estimate's precision varies by approximately 2.75% due to sampling variation. A smaller SE provides more assurance that the point estimate is a good reflection of the population truth.
Margin of Error
"Margin of Error (MOE)" is the buffer zone around your point estimate, indicating the range of the estimate with a high degree of confidence. It's calculated as the product of the critical value (often a Z-score in normal distributions) and the standard error. In our case, using a 95% confidence level, the Z-score is 1.96. The MOE is then:\[ MOE = 1.96 \times SE \approx 1.96 \times 0.0275 \approx 0.0539 \]This tells you that the range of our estimate for the proportion of doctors in solo practice could deviate by about 5.39%, ensuring that our conclusions remain statistically valid within this range.
  • The margin provides flexibility and trust in our point estimate.
  • It allows for natural variations in random sampling.
Statistical Interpretation
The "Statistical Interpretation" of a confidence interval is pivotal in understanding what your data conveys about the population. A 95% confidence interval indicates that if we were to repeat this sampling process 100 times, about 95 of those intervals would contain the true population proportion. For this exercise, the confidence interval was calculated as:\[ CI = \hat{p} \pm MOE = 0.521 \pm 0.0539 \]This results in an interval of \[0.4671, 0.5749\].What this means is, with 95% confidence, the true proportion of all medical doctors who have solo practices lies between 46.71% and 57.49%. When you report such findings, as a news writer, it's essential to state:
  • The point estimate with the associated margin of error.
  • That approximately 52.1% of doctors might have solo practices, acknowledging a margin of error of 5.39%.
Thus ensuring that interpretations remain clear and contextually accurate, helping readers comprehend the survey results effectively.

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Most popular questions from this chapter

Myers-Briggs: Marriage Counseling Isabel Myers was a pioneer in the study of personality types. She identified four basic personality preferences, which are described at length in the book A Guide to the Development and Use of the Myers-Briggs Type Indicator by Myers and McCaulley (Consulting Psychologists Press). Marriage counselors know that couples who have none of the four preferences in common may have a stormy marriage. Myers took a random sample of 375 married couples and found that 289 had two or more personality preferences in common. In another random sample of 571 married couples, it was found that only 23 had no preferences in common. Let \(p_{1}\) be the population proportion of all married couples who have two or more personality preferences in common. Let \(p_{2}\) be the population proportion of all married couples who have no personality perferences in common. (a) Check Requirements Can a normal distribution be used to approximate the \(\hat{p}_{1}-\hat{p}_{2}\) distribution? Explain. (b) Find a \(99 \%\) confidence interval for \(p_{1}-p_{2}\). (c) Interpretation Explain the meaning of the confidence interval in part (a) in the context of this problem. Does the confidence interval contain all positive, all negative, or both positive and negative numbers? What does this tell you (at the \(99 \%\) confidence level) about the proportion of married couples with two or more personality preferences in common compared with the proportion of married couples sharing no personality preferences in common?

What price do farmers get for their watermelon crops? In the third week of July, a random sample of 40 farming regions gave a sample mean of \(\bar{x}=\$ 6.88\) per 100 pounds of watermelon. Assume that \(\sigma\) is known to be \(\$ 1.92\) per 100 pounds (Reference: Agricultural Statistics, U.S. Department of Agriculture). (a) Find a \(90 \%\) confidence interval for the population mean price (per 100 pounds) that farmers in this region get for their watermelon crop. What is the margin of error? (b) Sample Size Find the sample size necessary for a \(90 \%\) confidence level with maximal margin of error \(E=0.3\) for the mean price per 100 pounds of watermelon. (c) A farm brings 15 tons of watermelon to market. Find a \(90 \%\) confidence interval for the population mean cash value of this crop. What is the margin of error? Hint: 1 ton is 2000 pounds.

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