How these figures are computed
Two numbers drive every page in this volume. Both are derived from one public classification, and both have limits worth knowing before you act on them.
1 · The source
Everything here comes from ESCO, the European Skills, Competences, Qualifications and Occupations classification. ESCO describes about 3,000 occupations and 14,000 skills, and records which skills each occupation needs, marking every one required or optional. It is maintained by the European Commission and published openly.
No job adverts, no scraped salaries, no survey. Just the classification and what can be computed from it. That is a real limit and it is worth stating plainly: ESCO describes occupations as they are defined, not as any particular employer hires for them.
2 · Coverage
Coverage answers one question: of everything the target role asks for, how much does the starting occupation already involve? Required skills count in full, optional ones at 0.35, since missing a nice-to-have is not the same as missing a requirement.
Coverage is directional, and that matters more than anything else on this page. A generalist moving into a narrow speciality is not the same problem as the reverse, so the figure for A to B will usually differ from B to A. A symmetric similarity score would hide exactly the thing you came here to find out.
3 · Difficulty
Difficulty combines how much is missing with how hard the missing part is to acquire. ESCO labels each skill by how widely it is reused: transversal skills appear almost everywhere, occupation-specific ones appear in a single job. Ten transversal gaps are a much smaller problem than ten occupation-specific ones, and the score reflects that.
The result is a 0 to 100 figure in four bands:
4 · Which pairs are recorded
Not all 9,232,482 possible ordered pairs are worth a page. Pairs are dropped when the two occupations share too little to compare, and also when they overlap so much that the target is really the same job under another name, where the gap list would be empty and the page would say nothing. What remains, 15,303 records, are moves where there is genuinely something to report.
5 · What this is not
This is a record of skill overlap. It is not careers advice and not a prediction about hiring. It does not know that a particular field wants a particular certificate, that a market is oversupplied, or that you would enjoy the work. It cannot see your experience, only the occupation you named.
Treat the gap table as a starting point for your own research rather than a syllabus. The figures are honest about what they measure, which is the only claim this volume makes.