An observed pay gap is a single number. The story behind it is two numbers. Most pay equity conversations fall apart because the two numbers get treated as one.
The first number is the structural gap — the portion explained by objective, documentable factors that vary between the people being compared. Different roles, different tenures, different performance grades, different geographic adjustments. The directive treats these as legitimate explanatory factors when they are documented and applied consistently across genders.
The second number is the residual gap — what remains after the structural factors are accounted for. This is the portion the directive examines. Under Article 4, the burden of explanation falls here. Under Article 10, the trigger condition checks this — not the headline.
The two layers, side by side
The portion of the observed gap explained by documented gender-neutral factors. Tenure: longer-tenured employees earn more by design. Performance grade: differentiated performance produces differentiated pay. Role within category: different complexities within the same job family. Geography: documented cost-of-location adjustments. Each factor has a paper trail.
The portion that remains after structural factors are applied. The directive does not require this to be zero. It requires that the employer have analysed it and either justified it on additional objective grounds or addressed it through remediation. The residual is the part the joint pay assessment looks at first.
A 15% headline gap with a 13% structural component and a 2% residual is a very different number from a 15% headline gap with no documented structural decomposition. The directive accepts the first as defensible. It treats the second as un-analysed.
The four factors that explain most of the structural portion
Across European SMEs in the 100–500 FTE range, four factors typically account for the majority of the observed gap when properly documented:
How the decomposition is done
The methodology is not prescribed by the directive. It is constrained by three principles: transparent, documented, gender-neutral by design. Common approaches:
Layer-by-layer subtraction. Start with the overall gap. Subtract the portion attributable to each documented factor in sequence. After the layers are removed, what remains is the residual. The order matters less than the consistency of application — the same factor applied identically to women and men.
Per-category recalculation. Recalculate the gap within homogeneous cohorts — same role, same level, same tenure band, same geography. The within-cohort gap is closer to the residual; the difference between within-cohort and overall is structural.
Regression analysis. For larger samples, fit a model predicting pay from documented factors plus gender. The gender coefficient, with appropriate confidence intervals, approximates the residual. Useful when the population is large enough to support statistical inference.
The directive does not endorse any specific methodology. It requires that the chosen methodology be documented, gender-neutral by design, and applied consistently. The choice between layer-by-layer, per-category, and regression is a judgment call based on company size and complexity. What matters is that the methodology can be defended when challenged — the methodology itself is part of what Article 10 examines.
What the residual actually tells you
A residual close to zero, after rigorous decomposition, means the structural factors explain the observed gap. The pay decisions are operating within the documented framework; the framework happens to produce different averages because the factors themselves vary between genders.
A non-trivial residual, after rigorous decomposition, means one of three things:
- An additional structural factor exists that hasn't been documented. The work is to identify and document it. The residual shrinks as more factors are properly accounted for.
- The decomposition methodology has a flaw. Common: a factor applied inconsistently across genders (e.g., performance grades that themselves reflect implicit bias). The work is to refine the methodology.
- There is a genuine unexplained gap. The work is to remediate — through pay adjustment, role rebalancing, or process changes — and to document the action taken.
The first two are methodological. The third is structural. The decomposition is what distinguishes them.
The headline gap tells you what was observed. The residual tells you what was unexplained. The directive is interested in the second.
Where the diagnostic starts
Calculating the residual requires the structural factors to be documented first. The methodology lives upstream of the calculation. If tenure, level, performance, and geography are not consistently recorded with gender-neutral application criteria, the decomposition cannot produce a defensible residual.
The ReadinessCheck™ surfaces whether the upstream documentation exists — by axis of the directive's principal obligations. The decomposition methodology is a downstream artefact of the same foundation.
The methodology lives upstream of the residual.
ReadinessCheck™ takes about 20 minutes and requires no salary data. It produces an observational position view by axis — including the structural-factor documentation that any residual calculation depends on.
Start the ReadinessCheck →