Variance Components in Gage R&R

Understanding the breakdown of measurement variation sources and their practical implications for system improvement.

Variance Components Overview & Breakdown

Variance components analysis in Gage R&R separates the total observed variation into distinct sources, enabling targeted improvement actions. This decomposition helps identify whether measurement problems stem from equipment, operators, or their interactions.

Key Components:

• • Repeatability (EV): Equipment variation
• • Reproducibility (AV): Appraiser variation
• • Interaction: Operator-by-part effects
• • Part-to-Part: True product variation
• • Total Study: Overall measurement variation

Acceptance Criteria:

GRR Variance Formula Focus

Gage R&R variance from repeatability and reproducibility

= equipment (repeatability) variation

= appraiser (reproducibility) variation

Total study variation

GRR

= combined measurement system variation

= part-to-part variation

Percent GRR and number of distinct categories

%GRR

= percent of total variation from measurement system

ndc

= number of distinct categories the system can resolve

Reading the Variance Components Breakdown

Example Result & %GRR Interpretation

Diagnosing the Dominant Source:

• • High EV (>50% of GRR): Equipment/gage issues - calibrate or repair
• • High AV (>50% of GRR): Operator training or method inconsistency
• • Significant Interaction: Some operators struggle with specific parts - review procedure
• • Low Part Variation: Study parts may not represent full process range

ndc Guidance:

• • ndc ≥ 5: Measurement system adequate to distinguish parts
• • ndc < 5: System cannot reliably discriminate part-to-part variation
• • Low ndc combined with acceptable %GRR may still signal narrow part sampling

sixsigmacenter.com Implementation Guide

Example Data Layout for Variance Components Analysis

Standard Gage R&R data structure for variance components analysis. Requirements: Minimum 2-3 operators, 5-10 parts, 2-3 trials per part. Each measurement must be linked to specific operator, part, and trial for proper variance decomposition.

This is how your spreadsheet or CSV file should be structured before you upload it. Match the column names, keep one row per observation, and leave the analysis to the platform.