Rule — 4 tiers max, plain labels, visual scale, drivers shown

Rule: Use 4 tiers maximum with plain labels (Low / Moderate / High / Very High difficulty). Show the tier on a simple visual scale with the user's position highlighted. List the 3-5 inputs that drove it.

Why: (a) IPCC ladder + EU SmPC convention precedent (IPCC likelihood ladder — the calibrated tier convention in high-stakes science communication, EU Summary of Product Characteristics — defined frequency bands as a tier convention); (b) visuals reduce worry where text inflates it (Han et al. — visual uncertainty bars REDUCE worry where text INCREASES it); (c) "earned" tier is the single biggest credibility lever (The "earned tier" — credibility comes from showing the inputs that produced the result); (d) defends against verbal-label misinterpretation (Budescu et al. 2009/2014 — IPCC verbal terms interpreted REGRESSIVELY; numeric pairing fixes, Knapp et al. 2004 — EU verbal frequency labels cause dramatic overestimation of medical risk).

How to apply: Top-of-output: tier label + visual scale + 3-5 driver bullets ("Your market has many established competitors; your site is new; you have fewer than 10 reviews"). Defines the floor of presentation quality.