Math Problem Statement

What sample size should be obtained if we want to be within four percentage points with 96% confidence if we use an estimate of 48% obtained from a poll?

Solution

To determine the sample size required to achieve a specified margin of error with a given confidence level, we can use the formula for the sample size nn for estimating a population proportion. The formula is:

n=(Z2p(1p)E2)n = \left( \frac{Z^2 \cdot p \cdot (1 - p)}{E^2} \right)

where:

  • ZZ is the Z-score corresponding to the desired confidence level,
  • pp is the estimated proportion,
  • EE is the margin of error.

Given:

  • Confidence level: 96%
  • Margin of error: 4% (0.04)
  • Estimated proportion (pp): 48% (0.48)

First, find the Z-score for a 96% confidence level. For a 96% confidence level, the Z-score corresponds to the area in the tails of the normal distribution such that 2% is in each tail (100% - 96% = 4%, so each tail has 2%).

Using a Z-table or standard normal distribution table, the Z-score for 96% confidence is approximately 2.05.

Now, plug these values into the formula:

n=(2.0520.48(10.48)0.042)n = \left( \frac{2.05^2 \cdot 0.48 \cdot (1 - 0.48)}{0.04^2} \right)

Calculate the components step by step:

  1. 2.052=4.20252.05^2 = 4.2025
  2. 0.48(10.48)=0.480.52=0.24960.48 \cdot (1 - 0.48) = 0.48 \cdot 0.52 = 0.2496
  3. 0.042=0.00160.04^2 = 0.0016

Now, compute the sample size:

n=(4.20250.24960.0016)n = \left( \frac{4.2025 \cdot 0.2496}{0.0016} \right)

n=(1.0494520.0016)n = \left( \frac{1.049452}{0.0016} \right)

n=655.9075n = 655.9075

Since the sample size must be a whole number, round up to the next whole number:

n656n \approx 656

Therefore, the sample size required is 656.

Would you like more details or have any questions about this calculation?


Here are 8 relative questions that expand on this information:

  1. What is the Z-score for a 95% confidence level?
  2. How does the margin of error affect the sample size?
  3. What happens to the sample size if the estimated proportion pp is closer to 0.5?
  4. How can we determine the Z-score without a Z-table?
  5. What is the formula for determining sample size for a population mean?
  6. How does increasing the confidence level affect the required sample size?
  7. What is the impact of a smaller margin of error on the sample size?
  8. How would the sample size change if the confidence level was increased to 99%?

Tip: Always round up the calculated sample size to ensure the margin of error is not exceeded.

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Math Problem Analysis

Mathematical Concepts

Statistics
Confidence Intervals
Normal Distribution

Formulas

Sample size formula for population proportion

Theorems

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Suitable Grade Level

Advanced High School