Example SOP for Rounding of Analytical Results

In short: This is an example SOP showing how a QC laboratory can round observed or calculated results before comparing them with a stated limit. The core idea is to calculate with unrounded values, round only the final result, and round to the same number of decimal places as the limit. It is an illustrative template, so adapt it under your own quality system and the pharmacopoeia that applies to your product.

Using this template

This page is an example SOP. It is not a regulatory requirement and not a ready-to-sign document. Your site’s SOP must follow your approved quality system, the compendium named in your product specification, and your change-control process. Items marked “example in-house criterion” are site practices, not compendial rules.

The rounding method below follows the approach in USP General Notices, section 7.20 (Rounding Rules). Other pharmacopoeias may word this differently, so follow the one that governs the test.

1. Objective

To describe how analytical results are rounded in the Quality Control laboratory, so that the rounded value is consistent with the limit expression and the safety, identity, strength, purity and quality of the product are not affected by the rounding step.

2. Scope

This SOP applies to results generated or calculated in the Quality Control laboratory of the manufacturing facility when they are compared with a specification limit.

3. Responsibility

• Analyst (or designee): follows this SOP when reporting results.
• Head of Quality Control (or designee): ensures the SOP is implemented and that analysts are trained.

4. Procedure

4.1 Rounding a result to compare it with a limit

1. Observed or calculated values usually carry more digits than the limit expression. Round the final result to the same number of decimal places as the limit.
2. Look only at the first digit to the right of the last place in the limit expression.
3. If that digit is less than 5, drop it and leave the preceding digit unchanged.
4. If that digit is 5 or more, drop it and increase the preceding digit by one.
5. Compare the rounded value with the limit. The limit itself is a fixed number and is never rounded.

4.2 Worked examples

4.3 Calculation and recording

1. During calculation, use the exact (unrounded) values. Round only the final reported value.
2. Intermediate values (for example a slope or a mean) may be shown rounded in a report, but the unrounded value is used in any further calculation.
3. Record both the unrounded value and the rounded value side by side in the raw data (example in-house criterion).

4.4 Values that are not rounded (example in-house criterion)

The following are site practices. Check each against the test method in your own specification.

1. Disintegration time is recorded in minutes and seconds.
2. Dissolution time is recorded in minutes.
3. pH is recorded as displayed on the pH meter.
4. Specification limits, being fixed numbers, are not rounded.
5. During balance calibration with standard weights, the weight displayed to the last decimal is recorded without rounding.
6. When weighing a test sample or working standard, the weight shown to the last decimal is recorded without rounding.
7. Volumetric solution strength is rounded to four decimal places, for example 0.001468 N is recorded as 0.0015 N.

5. Training

• Trainer: Head, Quality Control.
• Trainees: QC chemists and sectional heads.

6. Distribution

• Controlled copy 1: Head, Quality Assurance
• Controlled copy 2: Head, Quality Control
• Original copy: Quality Assurance

7. Annexures

Nil.

8. Abbreviations

• QC: Quality Control
• SOP: Standard Operating Procedure
• USP: United States Pharmacopeia

9. Revision history

Frequently asked questions

When should I round a result?

Only once, at the end, after all calculations are complete. Rounding intermediate values and carrying them forward can shift the final result across a limit.

Is a limit such as 98.0 % ever rounded?

No. Limits are fixed numbers. The result is rounded to match the limit’s number of decimal places, not the other way round.

Does this replace the rounding rule in my pharmacopoeia or method?

No. Where a compendial chapter or validated method states its own reporting rule, that rule takes precedence over this example SOP.

How long should raw data showing the original and rounded values be kept?

Keep GMP records at least 1 year after the expiry date of the respective product batch (EU GMP Part I, Chapter 4, section 4.11, or 5 years after QP certification if longer; 21 CFR 211.180(a)), and longer if local law or the marketing authorisation requires.

See also

• SOP on calibration of equipments and instruments
• Records maintenance in the quality control laboratory
• Out of specification investigation Phase Ia and Ib (MHRA)

References

• United States Pharmacopeia, General Notices and Requirements, section 7.20 Rounding Rules (current USP-NF edition).
• European Commission, EudraLex Volume 4, EU GMP Part I, Chapter 4 Documentation, section 4.11 (record retention).
• US FDA, 21 CFR 211.180(a), General requirements for records and reports (eCFR).