3.1.1. Current Practices in Specifying the Modeling Approach

Although the choice of modeling approach (ALCA or CLCA), which depends on the goal, clearly determines the outcome of an LCA study, our text-mining process found that the keywords "attributional" and "consequential" were missing in 75% of the LCAs involving multifunctional systems (see Figure 3 for a detailed breakdown, per product sector). This percentage refers only to the portion of articles published after 2004 when the term consequential LCA was clearly established (see Section 4.3). There are several possible reasons for this low specification rate of the modeling approach: (1) practitioners could still not be aware of the relevance to differentiate between consequential and attributional approaches, (2) practitioners may not specify the modeling approach because it is a direct consequence of the goal description, (3) they may not agree with a strict distinction between ALCA and CLCA, (4) they may be strictly following current ISO standards that do not distinguish between the two approaches or (5) they may have followed the recommendations of a policy directive or national/international guide that does not make such a distinction. Actually, some ALCA studies combined with consequential thinking are emerging [10]. These approaches aim mainly at accounting for some specific counterfactual effects or credits, and at the same time, limit complexity and uncertainties [59].

**Figure 3.** Percentage of articles which applied on the same case study both CLCA and ALCA approaches (Both), self-declared attributional studies (ALCA), self-declared consequential studies (CLCA) and studies which did not declare the approach followed (Not specified). Only case studies published after 2004 were considered (504).

The text-mining process found that 31% of the self-declared ALCA studies (using the keyword "attributional") used substitution as a system expansion approach to avoid allocation. However, this percentage varies depending on the sector under consideration, ranging from 19% to 45% (see Figure 4). The highest rate of substitution approaches in ALCAs was found in studies related to bio-based materials (45%). On the other hand, there are few LCAs investigating fossil products that self-declared as attributional studies. The reason might be that substitution is rarely an option for fossil products since they are usually the "substituted products".

**Figure 4.** Percentages of self-declared attributional studies (ALCAs) which applied substitution as a system expansion approach. Only the sectors with a significant amount (more than 10) of self-declared attributional studies are included in this graph.
