*4.2. Step 2: Listing the Items That Drive Complexity*

#### 4.2.1. Collection of the Factors Related to Complexity

Experts collected the factors that in their opinion could impact TURBT. All suggested items were considered and organized into domains, consistent with the medical usage and segmented according to the literature into a comprehensive list of items.

#### 4.2.2. Delphi Validation

The panellists scored the items using a five-point Likert scale, classifying from "very unlikely" to "very likely" the risk of complexity entailed by the individual items (Table 5). After the first Delphi round, they were informed of the panel's distribution of the scores and requested in the second round to confirm or adjust their personal evaluation.

Consensus on an item was reached when the opinions across the panel were so consistent that the 95% confidence interval of their distribution was bounded within two consecutive scores. In subsequent analyses, the median value of the opinions or Median Opinion (MO) was used to weight the contribution of an item to complexity.


