1. What is Sample Size Calculation Using Median?

This calculator provides an approximate sample size calculation when planning studies where the median will be used as the primary measure of central tendency. It uses a modified version of the standard sample size formula adjusted for median-based analysis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( n \) — Required sample size
• \( Z \) — Z-score for desired confidence level (1.96 for 95% CI)
• \( \sigma \) — Standard deviation of the population
• \( d \) — Margin of error (precision)

Explanation: This formula provides an approximate sample size needed to estimate the median with specified precision and confidence level.

3. Importance of Sample Size Calculation

Details: Proper sample size calculation ensures your study has adequate power to detect meaningful effects while avoiding unnecessary resource expenditure on overly large samples.

4. Using the Calculator

Tips:

• For 95% confidence, use Z = 1.96
• Standard deviation can be estimated from pilot data or literature
• Margin of error should reflect your desired precision
• All values must be positive numbers

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this for median calculations?
A: This provides an approximation. For exact median calculations, more complex methods may be needed.

Q2: What Z-score should I use?
A: Common values: 1.645 (90% CI), 1.96 (95% CI), 2.576 (99% CI).

Q3: How to estimate standard deviation?
A: Use pilot data, similar studies, or literature values. For new measures, consider a range of plausible values.

Q4: What if my data isn't normally distributed?
A: This formula works best for approximately normal distributions. For highly skewed data, consider non-parametric alternatives.

Q5: Should I adjust for expected dropout?
A: Yes, increase your calculated sample size by your anticipated dropout rate (e.g., if n=100 and 10% dropout expected, recruit 111 participants).