Stratification

Technique of separating data into meaningful groups or layers (strata) to identify patterns or differences that might be hidden in aggregated data. One of the 7 QC Tools in the original Japanese version. Common stratification factors include time (shift, day, month), location (line, plant, region), operator, supplier, or product type. Reveals whether problems are uniform or concentrated in specific strata. Example: overall defect rate is 5%, but stratifying by shift reveals Shift 2 has 12% while others have 2%. Essential before root cause analysis to focus investigation.