When setting up your quality control program, one key decision is which sampling plan type to use. ISO 2859-1 offers three options: single, double, and multiple sampling. Each has distinct advantages depending on your product, supplier history, and risk tolerance.
Single Sampling: The Standard Choice
Single sampling is what most importers use. You inspect one sample of predetermined size and make an immediate pass/fail decision. It's simple, straightforward, and easy to explain to suppliers. For a lot of 3,200 units at Level II AQL 2.5, you inspect 200 units once. Find ≤10 major defects? Pass. ≥11? Fail.
Double Sampling: The Compromise
Double sampling allows a second chance. You inspect a first sample (smaller than single sample size). If results are clearly good or clearly bad, you decide immediately. If results are borderline, you inspect a second sample. Total inspection volume averages 20-30% less than single sampling when quality is consistently good or bad.
Multiple Sampling: For High-Volume Specialists
Multiple sampling extends the double sampling concept to 5-7 stages. It's rarely used in import QC because it requires complex tracking and supplier confusion. However, military and aerospace applications favor it for maximum efficiency.
Our Recommendation
For 95% of importers, single sampling is the right choice. It's easy to implement, easy to explain, and provides consistent results. Only consider double sampling if you have a very stable supplier with years of consistent quality data.