## Sample size calculation

Even for the most experienced researchers, determining the sample size to interview can be difficult. For this reason, we have prepared this web application that allows you to calculate the sample size and the relative confidence interval to be able to have a representative sample.

# Calculation of sample size

 Confidence level: 95% 99% Confidence interval: Universe Numerosity: Sample size: 0 1

# Calculation of confidence interval

 Confidence level: 95% 99% Sample size: Universe Numerosity: Percentage of the answer Confidence interval: 0

To obtain a representative sample of the target it is necessary to define a sample structure (through the stratification variables) and the sample size.

Defining the sample structure and the sample size is a very complex operation that depends on numerous factors.

For example, under some very restrictive conditions, it is possible to calculate the sample size with a simple program.

This program is used to calculate:

• How many interviews to carry out in order to have a representative sample (under some constraints).
• The level of precision achieved with your sample.

To use this program you must have clear two concepts:

• Confidence interval
• Confidence level

## Confidence interval

Example: in your sample 38% answered a certain question "Yes". If you have an 5 confidence interval (i.e. of 5%) it will mean that the percentage of people who would answer "Yes", in the event that you interviewed the whole population, would be between 33% (38% -5 %) and 43% (38% + 5%).

## Confidence level

It represents how much you want to be sure of the result.

Example:continuing with the previous example, putting the level of confidence at XNUMX% will mean that with a XNUMX% probability the percentage of people who would answer "Yes", in the event that you interviewed the whole population, would be between XNUMX% (XNUMX % -XNUMX%) and XNUMX% (XNUMX% + XNUMX%).

The number of a sample is calculated assuming a certain confidence interval (typically 5%) and a certain level of confidence (typically 95%).

In order to calculate the sample size, you have to establish these two values first.  