![A simple trick to construct symmetric intervals Illustration of the 68-95-99.7 rule](https://blogs.sas.com/content/iml/files/2017/04/interval4-640x336.png)
Many intervals in statistics have the form p ± δ, where p is a point estimate and δ is the radius (or half-width) of the interval. (For example, many two-sided confidence intervals have this form, where δ is proportional to the standard error.) Many years ago I wrote an article