Sampling Size Calculation -

For a large or unknown population, use this standard equation:

A default "n=100" is almost never correct. While 100 is fine for a pilot or exploratory study, it provides a margin of error of ±9.8% (assuming 50% proportion, 95% confidence). That is nearly useless for decision-making.

Usually set at . This represents the probability that the test correctly rejects the null hypothesis. If power is 80%, you have an 80% chance of detecting an effect if one truly exists. C. Effect Size sampling size calculation

If you run 20 different statistical tests on the same dataset, you will find a "statistically significant" result purely by chance (due to a Type I error). If you plan to test multiple hypotheses, you must adjust your significance level (e.g., using Bonferroni correction: α = 0.05 / 20 = 0.0025). This, in turn, .

: Your (precision), expressed as a decimal (e.g., 0.05 for 5%). How to Determine Sample Size for a Research Study - GeoPoll For a large or unknown population, use this

[ n = \left( \fracZ \times \sigmae \right)^2 ]

Your e-commerce site has a 10% conversion rate (p1=0.1). You implement a new checkout design. You expect the new conversion rate to be 12% (p2=0.12). You want 80% power and 95% significance. Usually set at

This article is your definitive guide. We will dissect the statistical theory, walk through the formulas, provide real-world examples, and explore the software tools that make modern sample size determination possible.