Calculadora de Tamaño de Muestra Gratis
Determina el tamaño de muestra necesario para tu estudio según nivel de confianza y margen de error.
Sample Size (exact)
96.0400
Sample Size (exact) vs Z-Value (e.g., 1.96 for 95%)
Fórmula
## How to Calculate Required Sample Size ### Formula **n = (z * sigma / E)^2** where E is the desired margin of error, z is the critical value for the confidence level, and sigma is the population standard deviation. Always round up to the next whole number since you cannot have a fractional observation.
Ejemplo Resuelto
You want a 95% CI with margin of error 3 and estimated SD 15. How many observations are needed?
- 01n = (z * sigma / E)^2
- 02n = (1.96 * 15 / 3)^2
- 03n = (9.8)^2
- 04n = 96.04
- 05Round up: n = 97 observations needed
Preguntas Frecuentes
What if I do not know the population standard deviation?
Use a pilot study estimate, prior research, or the range/4 rule (approximate SD as the data range divided by 4). For proportions, use p = 0.5 for the most conservative estimate.
Why do we always round up?
Rounding down would give a sample slightly too small, resulting in a margin of error slightly larger than desired. Rounding up ensures the margin of error requirement is met or exceeded.
How does doubling precision affect sample size?
Halving the margin of error requires quadrupling the sample size, since n is proportional to 1/E^2. Precision is expensive in terms of sample size.
Aprender