When researchers use quantitative research methods and are confronted with a heterogeneous diversity of outcome variables, they might opt for conventional expert led approaches, which introduce quantification over multiple outcome variables. However, this strategy will only work in specific situations, where one can reasonable use a common metrics for uniform quantification over the outcome variables to fit them into the same model.
In response to this challenge, researchers in various disciplines have developed so-called multi-criteria analysis tools. In these tools, data is gathered for multiple outcome variables, without however using one single metric or calculus to find the most optimal system outcomes. Instead, the research produces quantitative assessments for a variety of chosen variables that represent issues of interest to the social actors, without using a common yardstick to measure them, such as economic outcomes, subjective well-being or aesthetic appreciation. These results are then used to inform the debate amongst the social actors on the best available action strategies.
Ongoing urban exploitation is increasing pressure on urban green spaces, while there is increasing awareness that greenery provides a range of important benefits to city residents. However, in their effort to preserve or introduce greenery, decision makers are confronted to choices to make amongst the many services that can be provided, such as recreation in dedicated areas, cooling of streets and public squares through spreading more “informal” greenery throughout the city or the more functional uses of urban green such as flood management. In addition, decision makers have to balance investments in services related to urban green with other services such as transport, improving access to housing and culture.
In efforts to help to understand the value of the various services provided by urban green, the researches of the transdisciplinary consortium Mistral Urban Futures developed a multi-criteria assessment of the value and benefits of urban green in the city of Gothenburg (Andersson-Sköld et al., 2010).
Figure. Left: cooling effect of urban green, images taken in a 2017 heatwave (source: city of Melbourne); Right: Urban green for flood risk management (source: Atelier PRO Architecten, project on Urban Green-Blue Grids for resilient cities).
The Gothenburg multi-criteria assessment was based on a “cascade” model. First, the researchers quantified a set of indicators of urban green with values collected in the seven case study area (bees abundance, diversity of songbirds, number of tree species, etc.). Second, the effectiveness of each of these indicators in producing the desired services illustrated in figures x are calculated by adding an effectiveness factor for each of the indicators, based on available meta-analyses in the literature. Finally, the overall value is obtained by multiplying the effectiveness with the weights attributed by the social actors.
A major challenge in multi-criteria quantitative analysis is to prioritize the various outcome variables in a transparent manner. In the Gothenburg study, the researchers used two complementary tools, which are a workshop with civil servants and interviews with citizens in the city. Through these tools, the aim was to understand the perceived importance for the social actors of a set of key services as illustrated in figure 5. The perceived importance was constructed by pairwise comparison amongst the services, with a scale from 1 to 5. In addition of a pairwise comparison amongst the services, a second questionnaire conducted a pairwise comparison of each the services related to urban green with other important services in the city such as transport and housing.