Calculadora de Tamanho de Amostra

The sample size calculator determines the minimum number of observations needed in a survey to estimate a population parameter with a specified confidence level and margin of error. It is based on the formula n = (z·σ/E)², where n is the sample size, z is the critical value from the normal distribution corresponding to the confidence level (e.g., 1.96 for 95%), σ is the population standard deviation (or an estimate), and E is the desired margin of error. The formula assumes a large population and simple random sampling.

To use the calculator, you need to enter the confidence level (90%, 95%, or 99%), the estimated standard deviation, and the acceptable margin of error. The result is the minimum sample size rounded up. For example, if you want to estimate average height with 95% confidence, a 2 cm error, and a standard deviation of 10 cm, the required sample is (1.96·10/2)² ≈ 96 people. This tool is essential in opinion polls, market research, clinical trials, and statistical surveys.

Important considerations: the population standard deviation is rarely known; use an estimate from previous studies or conduct a pilot test. The formula assumes a normal distribution and random sampling; if the population is small, adjustments like finite population correction may be needed. Also, very small margins of error dramatically increase sample size, raising costs. The calculator does not replace full sampling design, which should consider stratification, clustering, or other methods.