# CONFIDENCE.NORM

The `CONFIDENCE.NORM` formula is a statistical function that calculates the confidence interval for a given population mean, based on a normal distribution. It is commonly used to determine the sample size required to estimate a population mean within a specific margin of error with a given level of confidence.

## Usage

Use the `CONFIDENCE.NORM` formula with the syntax shown below, it has 3 required parameters:

Parameters:
1. alpha (required):
The significance level used to calculate the confidence interval. It must be a number between 0 and 1.
2. standard_deviation (required):
The population standard deviation. It must be a positive number.
3. pop_size (required):
The size of the population. It must be a positive integer.

## Examples

Here are a few example use cases that explain how to use the `CONFIDENCE.NORM` formula in Google Sheets.

### Estimating sample size for a survey

You want to conduct a survey to estimate the average income of a population with a margin of error of \$100 and a 95% level of confidence. You can use the `CONFIDENCE.NORM` formula to determine the required sample size.

### Estimating production yield

You are responsible for quality control in a factory and want to estimate the average yield of a production process with a margin of error of 2% and a 99% level of confidence. You can use the `CONFIDENCE.NORM` formula to determine the required sample size.

### Estimating student performance

You want to estimate the average grade of a student population with a margin of error of 0.5 and a 90% level of confidence. You can use the `CONFIDENCE.NORM` formula to determine the required sample size.

## Common Mistakes

`CONFIDENCE.NORM` not working? Here are some common mistakes people make when using the `CONFIDENCE.NORM` Google Sheets Formula:

### Not specifying alpha

If alpha is not specified, the formula will return a confidence interval with a default alpha of 0.05. To specify a different alpha value, make sure to include it as the first argument in the formula.

### Using sample standard deviation

CONFIDENCE.NORM requires the population standard deviation as an input, not the sample standard deviation. To calculate the population standard deviation, use the STDEVP function.

### Incorrectly specifying population size

Make sure to correctly specify the population size as the third argument in the formula. If the population size is unknown, use a large number such as 1000000.

The following functions are similar to `CONFIDENCE.NORM` or are often used with it in a formula:

• `STDEV.P`

The `STDEV.P` function is a statistical function that calculates the standard deviation of a population based on a sample of numerical data. It is commonly used to measure the amount of variation or dispersion in a dataset. The formula assumes that the input values represent the entire population, rather than a sample. If the input values represent a sample, you should use the `STDEV.S` function instead.

• `AVERAGE`

The AVERAGE function calculates the average (arithmetic mean) of the values passed to it. It is commonly used to find the average of a range of cells containing numerical data.

• `NORM.INV`

The `NORM.INV` function returns the inverse of the cumulative normal distribution for a specified mean and standard deviation. It is commonly used in statistical analysis to find the value at which a specified percentage of observations occur below that value.

You can learn more about the `CONFIDENCE.NORM` Google Sheets function on Google Support.