The measurement problem is not analytical. It is that the numbers most easily produced are the least persuasive to the people approving budget.
Rankings are an input, not an outcome
No finance director has ever approved spend on average position. The chain runs from rankings to impressions to clicks to conversions to revenue, and the business case has to be made at the revenue end while the reporting usually stops at the first link.
Attribution will undercount you
Organic search frequently starts the journey and gets no credit under last-click, so SEO is systematically undervalued in exactly the reports used for budgeting. Raise this before presenting numbers, not after someone challenges them, or it reads as an excuse.
The paid equivalent is the most portable framing
Value organic traffic at what the same clicks would cost through paid search for the same terms. It is imperfect — intent and click-through differ — but it converts organic performance into a currency the rest of the business already uses, which no other framing does as cleanly.
Report the lag honestly
SEO investment made this quarter shows up two or three quarters later. A business case that implies otherwise will be judged against a timeline it cannot meet. Stating the lag up front is what makes the eventual results credible rather than convenient.