RSD requirement for different sample size for blend sampling
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Updated: Oct 10, 2026

Sampling Soils in a Heterogeneous Research Plot
Published on: January 7, 2019
1Ortho-McNeil Pharmaceutical, Raritan, NJ 08869, USA.
Abstract:
A formula for calculating the equivalent relative standard deviation (RSD) for different sample sizes other than the Office of Generic Drugs (OGD) draft guidance was derived. These critical values vary with the population RSD and the sample size and guarantee the same confidence of passing a batch similar to the OGD blend uniformity test. Simulation results showed that the normal approximations give very close results to the simulation results. An assessment of the proposed OGD blend uniformity criteria against the first-stage USP content uniformity (CU) criteria for tablets was also made.
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