ISO 3086:2006

Overview

ISO 3086:2006 - "Iron ores - Experimental methods for checking the bias of sampling" defines statistical and experimental procedures to determine whether a sampling method for iron ores is biased compared with a reference stopped-belt sampling method (per ISO 3082). The standard explains how to design paired-sample experiments, compute differences, test for outliers and build confidence intervals to decide if a candidate routine sampling procedure has an acceptably small bias.

Key topics and requirements

• Reference method: A stopped-belt sampling method in accordance with ISO 3082:2000 is used as the unbiased reference (method A).
• Test method: The method under test (method B) - e.g., moving-belt samplers, ship/wagon transfer sampling - is compared against method A on the same material.
• Minimum data: At least 10 paired sets of measurements are required. Additional tests may be needed depending on outliers and statistical results.
• Pre-test inspection: A mechanical inspection of the sampling system is recommended before conducting bias tests.
• Data analysis steps:
  • Compute paired differences (d = xA − xB), mean (d̄) and standard deviation (Sd).
  • Apply Grubbs’ test to detect outliers; follow rules for reinstating/excluding outliers based on assignable causes and the proportion of remaining data (minimum retained percentage considered).
  • Determine a confidence interval for the mean difference using Student’s t (the standard recommends assessing a 90% confidence interval for the true average bias).
• Decision rule: Compare the confidence interval for the average bias to a pre‑defined relevant bias (δ). If the CI lies entirely within ±δ, method B is acceptable; if CI excludes zero, method B is biased and must be adjusted; if CI includes zero but extends beyond ±δ, further sampling is required.

Practical applications

• Establishing QA/QC for mine sampling programs and bulk material trading where accurate iron content, moisture, size distribution or other quality characteristics are critical.
• Validating new mechanical samplers, transfer-point sampling procedures, or modified sampling systems to ensure no systematic bias versus stopped-belt reference.
• Investigating differences between sampling locations (e.g., loading vs unloading) or testing sample-preparation and sieving bias when used with the corresponding ISO methods.

Who uses this standard

• Mining sampling engineers and metallurgists
• Laboratory managers and analysts responsible for sample preparation and assay QA/QC
• Quality assurance auditors, commodity traders and material buyers/sellers assessing contractual sampling risk

Related standards

• ISO 3082:2000 - Sampling and sample preparation procedures (reference sampling methods)
• ISO 3085:2002 - Experimental methods for checking precision of sampling and measurement
• ISO 4701 - Hand sieving methods (relevant where size distribution bias is tested)

Keywords: ISO 3086:2006, iron ores sampling bias, stopped-belt sampling, Grubbs' test, confidence interval, statistical test for bias, ISO 3082, ISO 3085.