On using an approximate noncentral t-distribution in determining a one-side upper limit for future sample relative reproducibility standard deviations.

For future sample relative reproducibility standard deviations (RSD(R)), collaboratively obtained under a completely randomized model (CRM), a new formula for determining a one-tailed 100p% upper limit (kappap) for such RSD(R) values was developed based on an approximate noncentral t-distribution with degrees of freedom obtained using Satterthwaite's adjustment. The accuracy of kappap was assessed by comparing kappap and its probability levels with similar values associated with a Monte Carlo simulation and with those obtained using another formula (gammap) that was developed for the same purpose but based on a normal approximation.