n proporção (margem E)
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The sample size calculator by proportion (margin of error) is a useful tool for determining the sample size required in statistical research. It uses the formula z²·p(1−p)/E² to calculate the sample size, where z is the z-score value, p is the expected proportion, and E is the desired margin of error.
Here, you can input the values of z, p, and E to calculate the sample size. This is especially useful in opinion polls, where the margin of error is crucial to ensure the accuracy of the results.
Remember that the choice of sample size is critical to the validity of research conclusions. An insufficient sample size can lead to inaccurate results, while an excessive sample size can be inefficient in terms of resources. Therefore, it is essential to choose the correct sample size.
Additionally, you should be careful when choosing the values of z and p, as they can significantly affect the sample size. For example, if you are working with a small population, it is better to choose a lower z value to avoid a very large sample size.
Frequently asked questions
What is the z-value?
The z-value is a measure of the distance between the estimate and the true population. It is calculated based on the normal distribution and is used to determine the desired margin of error.
What is the difference between expected proportion (p) and real proportion?
The expected proportion (p) is an estimate of the proportion of the population that has a certain characteristic. The real proportion is the true proportion of the population that has that characteristic.
Why is it important to choose a low margin of error?
A low margin of error means that you are more confident in the results of the research. However, it's essential to remember that a very low margin of error can be impossible to achieve with a reasonable sample size.
Can I use this calculator for opinion polls?
Yes, this calculator can be used for opinion polls. However, it's essential to remember that the choice of sample size must be made carefully, considering the desired margin of error and the accuracy of the results.
What is an insufficient sample size?
An insufficient sample size is when the sample size is too small compared to the population. This can lead to inaccurate and inconclusive results.