The CONFIDENCE.NORM function in Excel is a powerful tool that helps users determine the confidence interval for a population mean. This function is particularly useful in statistics and data analysis, as it assists in making inferences about the population from which a sample is drawn. By providing a range likely to contain the population mean, this function aids in decision-making and hypothesis testing.

Syntax

CONFIDENCE.NORM(alpha, standard_dev, size)

• alpha: The significance level used to calculate the confidence interval (1 minus the confidence level). For example, a 95% confidence interval would use 0.05.
• standard_dev: The standard deviation of the population from which the sample is drawn.
• size: The size of the sample drawn from the population.

Example #1

=CONFIDENCE.NORM(0.05, 2, 30)

This formula calculates a 95% confidence interval for a sample mean with a standard deviation of 2 and a sample size of 30. The result might be approximately 0.73, indicating that the true population mean is expected to lie within this range.

Example #2

=CONFIDENCE.NORM(0.01, 1.5, 50)

In this example, the function computes a 99% confidence interval for a mean, given a standard deviation of 1.5 and a sample size of 50. The result might yield a width of about 0.42, suggesting a narrower range due to the more stringent confidence level.

Example #3

=CONFIDENCE.NORM(0.10, 3, 100)

Here, a 90% confidence interval is calculated for a sample mean with a standard deviation of 3 and a sample size of 100. The result might be around 0.56, indicating broad confidence but still valuable for statistical analysis.

Error handling

• NUM!: Occurs when any argument is invalid, for instance, if size is less than 1.
• VALUE!: Appears when the inputs are of the wrong type, such as text instead of numbers.
• DIV/0!: Happens when the standard deviation is zero, which makes it impossible to calculate a confidence interval.

Conclusion

The CONFIDENCE.NORM function is an essential tool for statisticians and researchers who need to estimate the confidence intervals for the mean of a population. By understanding its syntax and proper usage, one can effectively make data-driven decisions based on statistical analysis.