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If we perform the activity *"Industrial processing and transformation"* **the probability of the receptor** *"Human health/wellbeing"* **is 0.474918, computed in 84.453**
seconds. This query takes longer than the previous ones because **the work** *"Industrial processing and transformation"* **has an influence on many more impacts**
than *"External movements of dangerous materials"* and *"Internal movements of* dangerous materials" **and all these influences must be combined to find the effect** on *"Human health and wellbeing"***. To give the reader an idea of the complexity of**
this query, there are 655,660 explanations, 12,847,036 atomic choices appear in the explanations and 42 random variables are involved.

The probability of receptor *"Atmosphere quality, microclimate"* **given the action**
"Industrial processing and transformation" **is 0.360851. The CPU time was 0.02s.**
If we add the activity *"Oil and gas extraction plants"* **the probability of the**
receptor *"Atmosphere quality, microclimate"* **lowers to 0.326481, computed in 6.852s**
By adding the activity *"Fire extinguishing plants"* **the probability of the receptor**
"Atmosphere quality, microclimate" **rises to 0.454471, due to the positive effects of** the last activity. The CPU time was 92.67 seconds.

As can be seen from the last three cases, increasing the number of **activities**
increases the computation time, since we have to combine the effects of the different causes. The last query has 606,726 explanations, 10,973,022 atomic **choices appear**
in the explanations and 36 random variables are involved.

## 6.3 Comparison

As hinted earlier, we developed two models with the final aim to integrate the two. Before such an ambitious goal can be reached, we need to identify strengths and weaknesses of the two. In order to have a systematic comparison, we produced two tables (one for each approach) in which each cell contains the effect of a single activity on a single receptor. One table reports the results of the linear model and the other those of the causal model. The tables are thus of size Na×Nr = 93×**23 =**
2139.

In the scatter plot of Figure 1 we draw the results of the causal model against those of the linear model: the linear model results are on the x-axis, while in the