Statistics
Interval bounds
The lower bound is the mean minus the margin and the upper bound is the mean plus it.
The Formula
mean +/- margin
The lower bound is the mean minus the margin and the upper bound is the mean plus it.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| lower | Lower bound | same as data | Bottom of the interval. |
| upper | Upper bound | same as data | Top of the interval. |
| mean | Sample mean | same as data | Centre of the interval. |
| E | Margin of error | same as data | Half the width of the interval. |
What Each Symbol Means
lowersame as data
Lower bound
Bottom of the interval.
uppersame as data
Upper bound
Top of the interval.
meansame as data
Sample mean
Centre of the interval.
Esame as data
Margin of error
Half the width of the interval.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate a confidence interval page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate A Confidence Interval, filed under Math. Every number the guide produces comes from substituting into this one line.