5.2.5. Normalization Process

All percentages for the process of normalization are shown in Figure 7. Eight studies used categorical rescaling [49,63,65,78,92,95–97], and five studies used continuous rescaling [7,67,68,86,94], with 47.1% and 29.4% of the total share, respectively. Three studies (17.6% of total) used a combination of both [48,90,93]. This option is not common, because this task would be confusing for non-expert stakeholders. On the other hand, only one framework (i.e., MIWABS [80]) used a different approach: the Proximity-to-Target [80], which happened to be a very close match to continuous rescaling, albeit with subtle, nuanced differences.

**Figure 7.** Percentage of Normalization Method.

#### 5.2.6. Weighting Process

The process of weighting indicators and components was seen in 15 of the 17 (90%) frameworks reviewed (Figure 8). Out of all the frameworks reviewed, the preference for allocating equal weights was dominant in eight studies [48,63,65,67,68,92,95,96] with a percentage of 47.1%. This aligns with the ethos of sustainability, which is about balancing, rather than trading off, respective pillars. Five studies [7,80,86,94,97] considered the non-equal weights (user-defined), with a percentage of 29.3% of the total. Only two frameworks [90,93] (11.8% of total) adopted a combination of both approaches.

5.2.7. Aggregation Technique and Final Index Value

The next element is the aggregation technique, which is used in combination with the weighting scheme in order to reach a final index value. Most frameworks [7,48,63,67,68, 78,80,86,92,94–97] (i.e., 14 or 82.35%) relied on the arithmetic technique—calculating the average rescaling value of indicators. The geometric technique was used twice: one time alone [90] and the other in combination with the arithmetic technique [93]. In contrast, the WEF nexus framework [49] used neither aggregation technique nor final index value.

In Figure 9, it can be seen that the most widely adopted interval for the final index value (with 41.2% of total) was 0 and 100 [48,67,68,80,86,90,93]. Therefore, it can be suggested that this interval was the most preferred choice for both experts and stakeholders within the frameworks reviewed. The second most widely adopted interval for final index value (with 23.5% of total) was 0 and 1 [7,63,65,94]. The third most widely adopted interval for final index value (with 17.6% of total) was 1 to 5 [78,92,95]. A category called "other" was used to combine any final index value with a unique range that appeared once in the frameworks reviewed. This happened in only two indices [96,97] (11.8% of total). The last category called "without" for the WEF nexus framework [49] (5.9% of total), which does not have any final index value. Meanwhile, only the final assessment for each indicator (or criterion as they called it) is provided with a qualitative description in an individual assessment card without aggregating all indicators or components to get a single final value.

**Figure 9.** Interval of Final Index Value.
