Calculation of an overall weighted score for each driver and ranking process
To obtain the overall score per driver, an aggregation method that combined the two types of weighting (i.e. the intra and inter-domain) was used. First, the driver score (coefficients attributed by experts) was standardised by dividing it by the number of possibilities. Indeed, some drivers were allocated coefficients from 0 to 4 (5 possibilities) and others from 1 to 4 (4 possibilities). Afterwards, this standardised score was multiplied by the intra-domain weight and the inter-domain weight, as given by the expert. These results allowed obtaining an overall weighted score for each driver and per expert:
OWSDri= SDri x WDri x WDoj [Equation 1]
In this formula, OWSDri = overall weighted score for a specific driveri ; SDri = standardized score for a specific driveri ; WDri = intra-domain weight for a specific driveri ; WDoj = inter-domain weight for a specific driveri included in a specific domainj .
Furthermore, all drivers were ranked based on the median overall weighted score obtained for each driver and taking into account the answers of all the experts, which answered the questionnaire.
The statistical difference of the median, depending of the specific driver or the group of drivers considered, was assessed through a non-parametric Kruskal-Wallis equality-of-populations rank test (State SE 14.2; StataCorp, College Station, Texas, USA).