@@ -18,6 +18,9 @@ Activity Browser has three contribution analysis approaches available to assess
1818` Elementary Flow (EF) Contributions ` , ` Process contributions ` and ` First Tier (FT) Contributions ` .
1919
2020Before we discuss the different approaches, we introduce a small example for the production of _ 'steel'_ :
21+ These approaches are extensively discussed independent of Activity Browser by
22+ [ van der Meide et al. (2025)] ( https://doi.org/10.31219/osf.io/sfgj6_v1 )
23+ if you want to learn more.
2124
2225![ steel production example] ( ./assets/steel_production_example.svg )
2326
@@ -33,7 +36,8 @@ The amounts we use are:
3336<b >Note:</b > These numbers are used for ease of understanding, not for realism.
3437</sup >
3538
36- To produce 1 kg of steel, we get a climate change impact of 1.6 kg CO2 eq with the _ 'IPCC 2021'_ impact category.
39+ To produce 1 kg of steel, we get a climate change impact of 1.6 kg CO<sub >2</sub > eq. with the
40+ _ 'IPCC 2021 GWP 100'_ impact category.
3741In the way Brightway (and thus Activity Browser) calculate results, a _ contribution matrix_ is calculated with
3842all impacts _ from_ all EFs and all activities.
3943For the system and functional unit above, this would be:
@@ -46,15 +50,15 @@ For the system and functional unit above, this would be:
4650The _ contribution matrix_ show the dis-aggregated results for each individual biosphere flow for each activity.
4751
4852#### Elementary Flow (EF) contributions
49- If we take sum the _ rows_ to one row , we get the EF contributions
53+ If we take the sum the _ rows_ to one column , we get the EF contributions
5054(the contribution of all CO<sub >2</sub > and CH<sub >4</sub > impacts together).
5155
5256In the case above, the EF contributions are:
5357- CO<sub >2</sub >: 1.5404... (96.3%)
5458- CH<sub >4</sub >: 0.0596... (3.7%)
5559
5660#### Process contributions
57- If we take the sum of the _ columns_ to one column , we get the process contributions
61+ If we take the sum of the _ columns_ to one row , we get the process contributions
5862(the contribution of all coal, electricity and steel production impacts together).
5963
6064In the case above, the process contributions are:
@@ -115,9 +119,19 @@ in the next sections.
115119![ contributions cutoff] ( ./assets/contribution_manipulation.png )
116120
117121#### Cut-off
118- You can manually change the ` Cut-off type ` of the results in two ways, ` Relative ` or ` Top # ` .
119- - The ` Relative ` mode shows contributions _ from_ entities of _ x_ % or higher.
122+ You can manually change the ` Cut-off type ` of the results in three ways:
123+ - The ` Minimum % ` mode shows contributions _ from_ entities of at least _ x_ % or higher.
124+ - For example: If the cut-off is set to 5% for process contribtions, then all contributions of at least 5% are shown.
125+ - The ` Cumulative % ` mode shows contributions that cumulatively contribute at least _ x_ %.
126+ - For example: If the cut-off is set to 80% for process contributions, then the first _ n_ processes (sorted highest
127+ to lowest) that count up to 80% are shown.
120128- The ` Top # ` mode shows contributions from the _ x_ entities that contribute the most (as absolute).
129+ - For example: If the cut-off is set to 5, then the first 5 processes (sorted highest
130+ to lowest) will be shown.
131+
132+ The cut-off is applied per item (e.g. per reference flow or impact category, see [ compare] ( #compare ) ) below).
133+ This means that if you want to see the top 5 contributors, you will only see the top 5 per item, even if a contributor would
134+ also be present for another item.
121135
122136You can adjust the ` Cut-off level ` to change how many results you see.
123137
@@ -147,22 +161,22 @@ You can disable one of them if you want to focus on the other.
147161
148162#### Relative and Absolute
149163You can choose between ` Relative ` and ` Absolute ` results.
150- The ` Relative ` results will sum to 100% (the total ` Range ` or ` Score ` ),
164+ The ` Relative ` results will sum to 100% (the total ` Score ` or ` Range ` ),
151165the ` Absolute ` results will sum to the impact score.
152- For ` Relative ` , you can choose what you use as the 100% reference, the ` Range ` or the ` Score ` .
166+ For ` Relative ` , you can choose what you use as the 100% reference, the ` Score ` or the ` Range ` .
153167
154- #### Range and Score
155- The ` Range ` /` Score ` determines what you use as the _ total_ to which the contributions are counted.
156- - For ` Range ` , this is the full _ range_ of results
157- - For example, if all your negative results together have a score of -2 and all your positive results together have a
158- score of 10, the _ range_ is 12 (-2 * -1 + 10).
159- - An entity with a contribution of 4 would have a relative contribution of 4/12 = 33.3...%.
168+ #### Score and Range
169+ The ` Score ` /` Range ` determines what you use as the _ total_ to which the contributions are counted.
160170- For ` Score ` , this is the total score (sum) of the results
161171 - For example, if all your negative results together have a score of -2 and all your positive results together have a
162172 score of 10, the _ score_ is 8 (-2 + 10).
163173 - An entity with a contribution of 4 would have a relative contribution of 4/8 = 50%.
174+ - For ` Range ` , this is the full _ range_ of results
175+ - For example, if all your negative results together have a score of -2 and all your positive results together have a
176+ score of 10, the _ range_ is 12 (-2 * -1 + 10).
177+ - An entity with a contribution of 4 would have a relative contribution of 4/12 = 33.3...%.
164178
165- The ` Range ` or ` Score ` setting are only relevant when your results contain both positive and negative contributions.
179+ The ` Score ` or ` Range ` setting are only relevant when your results contain both positive and negative contributions.
166180
167181### Positive and negative numbers in contribution results
168182It can happen in LCA that you get both positive and negative numbers in your contribution results.
@@ -179,9 +193,11 @@ Below is a simple example (with unrealistic values) to demonstrate this:
179193## Sankey
180194The ` Sankey ` tab shows results from [ graph traversal] ( https://docs.brightway.dev/projects/graphtools/en/latest/index.html ) .
181195Graph traversal calculates results step-by-step for _ nodes_ (activites) in the _ graph_ (supply chain/product system).
196+ This is explained in detail by
197+ [ van der Meide et al. (2025)] ( https://doi.org/10.31219/osf.io/sfgj6_v1 ) (path contributions).
182198
183199### Sankey configuration
184- In the ` Sankey ` tab, you can configure, you can set the
200+ In the ` Sankey ` tab, you can set the
185201Reference flow, Impact category and Scenario (only available in scenario LCA, see [ scenarios] ( #scenarios ) ) to be shown.
186202you can also set a ` cutoff ` and ` calculation depth ` setting.
187203
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