where "tk,p" and are the "p"th quantiles of the "t"- and "χ"2-distributions respectively. These confidence intervals are of the "confidence level" , meaning that the true values "μ" and "σ"2 fall outside of these intervals with probability (or significance level) "α". In practice people usually take , resulting in the 95% confidence intervals. The approximate formulas in the display above were derived from the asymptotic distributions of formula_362 and "s"2. The approximate formulas become valid for large values of "n", and are more convenient for the manual calculation since the standard normal quantiles "z""α"/2 do not depend on "n". In particular, the most popular value of , results in .