Math Problem Statement

A political candidate has asked you to conduct a poll to determine what percentage of people support her. If the candidate only wants a 1% margin of error at a 99% confidence level, what size of sample is needed? Give your answer in whole people.

Solution

To calculate the required sample size for this poll, we can use the formula for sample size in proportion estimation:

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 (for 99% confidence, Z=2.576Z = 2.576),
  • pp is the estimated proportion of people supporting the candidate. If we don't have a prior estimate, we use p=0.5p = 0.5 to maximize the sample size,
  • EE is the margin of error, which is 1% or 0.010.01 in this case.

Step-by-Step Calculation:

  1. Identify the Z-score: For a 99% confidence level, Z=2.576Z = 2.576.
  2. Assume proportion (p): We use p=0.5p = 0.5 as no prior data is given.
  3. Set margin of error (E): E=0.01E = 0.01.

Plugging in these values:

n=(2.576)20.5(10.5)(0.01)2n = \frac{(2.576)^2 \cdot 0.5 \cdot (1 - 0.5)}{(0.01)^2}

Calculating each component:

n=6.6350.50.50.0001n = \frac{6.635 \cdot 0.5 \cdot 0.5}{0.0001} n=1.658750.0001n = \frac{1.65875}{0.0001} n16587.5n \approx 16587.5

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

n=16588n = 16588

Answer:

The required sample size is 16,588 people.

Would you like more details on each step or further explanation?


Here are five related questions that expand on this concept:

  1. How would the required sample size change if the confidence level were 95% instead of 99%?
  2. What would happen to the sample size if we had a prior estimate that p=0.6p = 0.6?
  3. How does the margin of error influence the sample size requirement?
  4. Why do we use p=0.5p = 0.5 when there is no prior data?
  5. How is the Z-score determined for different confidence levels?

Tip: When estimating proportions, using p=0.5p = 0.5 provides the largest possible sample size, ensuring the estimate remains valid even in the worst case.

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Math Problem Analysis

Mathematical Concepts

Statistics
Sample Size Calculation
Confidence Interval
Margin of Error

Formulas

n = (Z^2 * p * (1 - p)) / E^2

Theorems

Central Limit Theorem

Suitable Grade Level

Undergraduate Statistics or AP Statistics