From the section on Significance Testing in onlinestatbook:

Whenever an effect is significant, all values in the confidence interval will be on the same side of zero (either all positive or all negative).

Why? Can’t a confidence interval be positioned both sides of the zero? Say, can’t its range be [-12; +12]?

**Answer**

Can’t a confidence interval be positioned both sides of the zero? Say, can’t its range be [-12; +12]?

Certainly it can.

Did you miss the stated condition “Whenever an effect is significant”?

**Attribution***Source : Link , Question Author : CopperKettle , Answer Author : Glen_b*