Welcome Mai.

Your question, while simple, has not easy answer. This is a complex topic that is not well understood by many. First sampling plan doesnt’ have a confidence **interval**. Confidence **intervals **are calculated after the sampling and inspection or test is complete. We need the number of defects found and the sample size adn the confidence **level** to calculate the interval.

Are you asking about the confidence level? For AQL plans taken from a published table, this is usually 95%. Btu we must remember that this is means (in your example) that 95% of the time when a defect rate of 1% is present, you will accept the lot.