Confidence Interval (CI)

What is Confidence Internal

A Confidence Interval is a range of values we are fairly sure our true value lies in.

We measure the heights of 40 randomly chosen men, and get a mean height of 175cm,

We also know the standard deviation of men's heights is 20cm.

The 95% Confidence Interval (we show how to calculate it later) is:

175cm ± 6.2cm

confidence interval 175 plus minus 6.2

How to calculate Confidence Internal

Step 1: find the number of samples n, calculate the mean X of those samples, and the standard deviation s Step 2: decide what Confidence Interval we want: 95% or 99% are common choices. Then find the "Z" value for that Confidence Interval here: Confidence Interval Z 80% 1.282 85% 1.440 90% 1.645 95% 1.960 99% 2.576 99.5% 2.807 99.9% 3.291

Step 3: use that Z in this formula for the Confidence Interval

X ± Z(s/√n)

Where:

X is the mean
Z is the chosen Z-value from the table above
s is the standard deviation
n is the number of samples