HKSM

Selecting a subset of a defined population for inspection so you can draw conclusions about the entire group.

Key Points

• Used to assess quality or performance without examining every item or instance.
• The sample must represent the population; common methods include random, systematic, and stratified sampling.
• Sample size depends on desired confidence level, margin of error, variability, and lot size.
• Reduces cost and time but introduces sampling risk; plan and document the approach in the quality management plan.

Example

A project produces 8,000 metal brackets each week. During Control Quality, the team randomly selects 300 brackets based on a sampling plan (95% confidence, 5% margin of error) and inspects them for dimensional accuracy. Results are used to accept the lot and adjust the process if defects exceed thresholds.

PMP Example Question

While performing Control Quality, the team wants to estimate the overall defect rate without inspecting every deliverable. What technique should they use?

1. Benchmarking
2. Statistical sampling
3. Checklists
4. Quality audit

Correct Answer: B — Statistical sampling

Explanation: Statistical sampling inspects a subset of outputs to infer the quality of the entire population, reducing effort while maintaining confidence.