# Confidence Interval Formula

The Confidence Interval used in statistics to describe the amount of uncertainty associated with a sample estimate of a population parameter. It describes the uncertainty associated with a sampling method.

Confidence interval is a range within which most plausible values would occur. To calculate confidence interval, one needs to set confidence level as 90%, 95%, or 99% etc. A 90% confidence level means that we would expect 90% of the interval estimates to include the population parameter; 95% of the intervals would include the parameter and so on.

Where,

n = Number of terms

x = Sample Mean

σ = Standard Deviation

$z_{\frac{\alpha }{2}}$ = Value corresponding to $\frac{\alpha }{2}$ in z table

$t_{\frac{\alpha }{2}}$ = Value corresponding to $\frac{\alpha }{2}$ in t table

$\alpha$ =1- $\frac{Confidence\;Level}{100}$.