In the first version of the practice notes, we suggested that to avoid over counting, impact could not be counted as extending past a year even if you collect data that indicates that the beneficiary continues to be in the improved state. This is because of the increasing level of deadweight that would occur over time (the proportion of people in your intervention who would have achieved the same outcome without your activity at some point over the coming years) and the need to keep the methodology accessible.
Now that understanding of the approach and data collection appears to have improved, we can develop the methodology to reflect the logic of an increasing deadweight. Currently, deadweight is applied to the value generated from an activity over a year to account for ‘what might have happened anyway’. To claim value in following years, it is logical to add the first year deadweight to the deadweight for subsequent years as in the table below:
|
Deadweight |
|
|
|
|
|
|
|
|
Year: |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
|
Training and employment |
15% |
30% |
45% |
60% |
75% |
90% |
100% |
|
Community and social |
19% |
38% |
57% |
76% |
95% |
100% |
100% |
|
Crime prevention |
19% |
38% |
57% |
76% |
95% |
100% |
100% |
|
Health |
27% |
54% |
81% |
100% |
100% |
100% |
100% |
This does not prevent you using the values in other impact valuation methodologies that do permit the use of informed judgments around duration and drop off. While increasing the deadweight is a logical approach, we would still like to hear about which interventions this process might be relevant to.
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