Calculate the sample size you need when your survey measures a proportion or a percentage (for instance, % of smokers in a population). Using this advanced calculator you will see how error margin, confidence level and sample size are interrelated. More information about the used formulas here.

To use the calculator:

- Enter the size of the universe and the degree of heterogeneity of the population.
- Enter 2 out of the 3 remaining parameters. For instance, if you indicate the sample size and the confidence, margin of error will be calculated.
- Press ‘Calculate’’. The resultant value will be highlighted.

Calculate the sample size you need when your survey measures an average value (for example, the average number of cigarettes smoked per individual in the population). In this advanced calculator you will be able to see how margin of error, confidence level and sample size are interrelated.

To use the calculator:

- Enter the size of the universe and the approximate variance that you expect for your data.
- Enter 2 out of the 3 remaining parameters. For instance, if you indicate the sample size and the confidence level, margin of error will be calculated.
- Press ‘Calculate’. The resultant value will be highlighted.

Check if the observed difference between two samples is significant regarding a percentage or a proportion. For example, you have two online advertisements to engage users in your web, A and B. You show each advertisement to 1.000 people and A advertisement gets 10,5% of sales conversion and B gets 11%. How can you determine if this difference was by chance or advertisement A was really better? By doing a test of significance. You have more info in the following post.

To use the calculator:

- Enter the sample size and the observed % for the sample 1.
- Do the same with sample 2.
- Enter which confidence level you want in order to prove that the observed difference is not by chance. A larger confidence level requires a larger observed difference.
- ...so there it is! Result is re-calculated each time you modify the different parameters. The calculator evaluates if the difference is significant and which is the minimum difference you have to observe to get this significance.

Check if the observed difference between two samples is significant regarding an average value. For example, you want to know if mothers from the country A have more children on average than mothers in country B. After surveying 1.000 mums from each country you get that mothers from country A have 2,4 children on average and mothers from country B a 3,1. How you can determine if the difference is due to sample size effects or it is real? By doing a significant test. You have more information in the following post.

To use the calculator:

- Enter the sample size, the observed mean and standard deviation for the sample 1.
- Enter which confidence level you want in order to prove that the observed difference is not by chance. A larger confidence level requires a larger observed difference.
- ...so there it is! Result is re-calculated each time you modify the different parameters. The calculator evaluates if the difference is significant and which is the minimum difference you have to observe to get this significance.

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