One-Sided One-Mean z-Intervals. Presuming that the assumptions for a one-mean z-interval are satisfied, we have the following formulas for (1 − α)-level confidence bounds for a population mean μ:

Lower confidence bound: x¯ − zα · σ/√n Upper confidence bound: x¯ + zα · σ/√n Interpret the preceding formulas for lower and upper confidence bounds in words.