50% confidence level vs. no confidence level

When using the equation Reliability = (n-r)/(n+1) is the answer at the 50% confidence level?

I and my various peers over the years have always considered that this reliability is at the 50% confidence level. But now I’m being asked for a reference stating that.

First is the 50% CL correct for this equation, and if so can anybody point me to a reference?

Thanks.