ICH Q2, the guideline from the International Council for Harmonisation (ICH), has governed analytical procedure validation for pharmaceutical registration since the mid-1990s. The revision, Q2(R2), was adopted by ICH in November 2023. Q2(R2) has applied in the EU since June 2024, and other regions adopted it on their own dates. A new companion guideline, Q14, covering analytical procedure development, arrived alongside it.
Together, Q2(R2) and Q14 move validation from a one-off study towards a lifecycle. Q14 defines what the procedure needs to achieve, and Q2 is the demonstration that it does.
Q14 introduces the analytical target profile (ATP): the performance the procedure must reliably deliver, stated in advance. The ATP matters for the statistics, because it answers a question that undermines much validation work: where the acceptance criteria came from. Under an ATP the criteria are set before the study, from what the measurement has to be capable of.
Which characteristics apply depends on what the procedure is for: an identification test, a quantitative or limit test for impurities, or an assay. The full set, and the analysis each rests on:
| Characteristic | The study, and the guide |
|---|---|
| Specificity / selectivity | Response attributable to the analyte alone: interference and recovery testing |
| Response (linearity, or a non-linear calibration model) | How the result relates to concentration across the range: fitting a calibration curve and assessing linearity |
| Range | The interval over which linearity, accuracy and precision all hold: the measuring interval |
| Accuracy | Closeness to the accepted value, usually by recovery or against a comparative procedure: trueness, precision and accuracy |
| Precision — repeatability | Variation within a run, under constant conditions: the precision components |
| Precision — intermediate | Variation within the laboratory across days, analysts and equipment: establishing precision |
| Precision — reproducibility | Variation between laboratories, from a collaborative study |
| Detection limit (a lower range limit) | The lowest concentration detectable, not necessarily quantifiable: LoB, LoD and LoQ |
| Quantitation limit (a lower range limit) | The lowest concentration measurable with acceptable precision and accuracy: the precision-profile method |
| Robustness | Tolerance of deliberate small changes in method parameters, usually established during development under Q14, before the validation study: robustness testing |
Anyone moving between pharmaceutical and clinical laboratory work meets the same quantities wearing different labels. The mismatch causes more confusion than the underlying ideas do.
| ICH Q2 | Clinical laboratory equivalent |
|---|---|
| Detection limit (DL) | Limit of detection (LoD), sitting above a limit of blank |
| Quantitation limit (QL) | Limit of quantitation (LoQ) |
| Intermediate precision | Within-laboratory precision |
| Reproducibility | Reproducibility, between laboratories (the same thing) |
| Specificity | Analytical specificity, interference and cross-reactivity |
| Range | Analytical measuring interval |
| Accuracy | Trueness, where accuracy means trueness and precision combined |
The last row is the one that causes real trouble. In the metrological vocabulary used across the clinical guidelines, accuracy is the combination of trueness and precision, and trueness alone is closeness to the reference value. In Q2(R2), accuracy on its own still means trueness. What the revision added is the option to judge accuracy and precision together, against one combined criterion. Check which approach the protocol uses before choosing the study.
Intermediate precision is defined as intra-laboratory variation, and the definition names its sources: different days, different analysts, different equipment, different environmental conditions. That structure is a multi-factor design, usually nested or partly crossed, and the analysis separates the variance contributed by each level rather than pooling them into one figure.
Reporting a single standard deviation for intermediate precision discards the breakdown by source. Knowing that between-day variation dominates and between-analyst variation is negligible tells you where to intervene; a pooled figure does not. See the precision components explained for how the levels separate, and establishing precision for the study design.
Q2(R2) is a full revision rather than an editorial update, clarifying the distinction between specificity and selectivity and extending coverage to procedures for biotechnological products. Non-linear response models and multivariate calibration models are now explicitly in scope, where the original had been written largely around a straight-line response. The revision also allows accuracy and precision to be evaluated together against a combined performance criterion, a total-error approach, instead of separately.
Q2(R2) also gives more attention to procedure transfers and to partial revalidation after a change. Read alongside Q14, the effect is that validation stops being a single event. The ATP defines the target, and development evidence can contribute to the validation package. Changes are managed against the same target rather than triggering a full revalidation each time.
Download the multi-laboratory precision example workbook (.xlsx): CA19-9 measured on six samples in three laboratories, five runs of five replicates each, ready to open in the Analyse-it trial. The analysis gives repeatability, within-laboratory precision and reproducibility for each sample, then fits a precision profile across the range. The example follows a clinical protocol (CLSI EP05-A3), but the same variance-components analysis serves intermediate precision and reproducibility.
The example workbook is downloading.
It opens in Excel on its own — the data and the finished results are both in it. Analyse-it is what lets you change the analysis and re-run it, try the same study on your own data, or work through it to see how the software handles it.
Every feature from all five editions for 15 days.
Setting acceptance criteria after the study. The ATP exists to prevent this. A criterion chosen once the data are in is not a demonstration of suitability for purpose.
Mixing the two meanings of accuracy. In ICH Q2, accuracy on its own means trueness, but Q2(R2) also allows accuracy and precision to be judged together against one combined criterion. Either is acceptable if the protocol says which before the study.
Pooling intermediate precision into one number. The breakdown by source is where the information is. Report the components.
Judging linearity by the correlation coefficient. It will be high for a curved response over a wide range. Read the residuals.
Testing robustness one factor at a time. It cannot find interactions, which are the failures that surprise people.
Analyse-it produces the statistics the Q2 characteristics rest on, inside Excel:
Every feature from all five editions for 15 days. Model fitting and multi-factor analysis are in every edition, from US$ 155 a year; the precision, linearity and detection capability analyses are in the Method Validation and Ultimate editions, from US$ 475 a year. Validated against NIST and CLSI reference datasets.