1. What is the Raosoft Sample Size Formula?

The Raosoft sample size calculator uses a standard statistical formula to determine the minimum number of respondents needed in a survey to achieve statistically significant results, based on your desired confidence level, margin of error, and population proportion.

2. How Does the Calculator Work?

The calculator uses the sample size formula:

Where:

• \( Z \) — Z-score (standard score for confidence level)
• \( p \) — Expected proportion (0.5 for maximum variability)
• \( e \) — Margin of error (acceptable error percentage)

Explanation: The formula calculates how many samples are needed to estimate a population proportion within a certain margin of error at a given confidence level.

3. Importance of Sample Size Calculation

Details: Proper sample size ensures your survey results are statistically valid and representative of the population while avoiding unnecessary data collection costs.

4. Using the Calculator

Tips:

• For 95% confidence level, use Z-score of 1.96
• Use p = 0.5 for maximum sample size (most conservative estimate)
• Common margin of error values are 0.05 (±5%) or 0.03 (±3%)
• Include population size for finite population adjustment

5. Frequently Asked Questions (FAQ)

Q1: What Z-score should I use?
A: Common values are 1.645 (90% CI), 1.96 (95% CI), and 2.576 (99% CI).

Q2: Why use 0.5 for proportion?
A: 0.5 gives the maximum sample size needed, as p(1-p) is largest when p=0.5.

Q3: How does population size affect sample size?
A: For small populations, the sample size can be adjusted downward using finite population correction.

Q4: What's a reasonable margin of error?
A: For most surveys, 5% is acceptable. For precise measurements, 3% or less may be needed.

Q5: Can this be used for non-survey research?
A: This formula is specifically for proportion estimation. Other formulas exist for means comparisons.