Table 1.

Cost categories

Cost category	Description and key assumptions
1. Formative research (software capital)	Design-focused research and piloting to identify target drivers of behaviours and the development of a comprehensive behaviour change strategy. It is conceptualised as a one-off investment with useful life of 1 year.
2. Promotion (software capital)	Hygiene promotion campaign with a useful life of 5 years, and modes of delivery including: (1) house-to-house visits by promoters; (2) community/group activities and (3) mass media (online supplemental material B).
3. Handwashing facility (hardware capital)	Purpose-built 20 litre drum with tap, basin and stand, with a useful life of 5 years. No capital maintenance is assumed, due to short useful life and very simple infrastructure.
4. Top-up promotion (software capital maintenance)	Additional promotion activities occurring annually at 25% of initial cost (an assumption based on expert judgement), representing a lighter version of the intervention with lower frequency and dose
5. Soap (recurrent)	Expenditure on soap for handwashing (ie, excluding other uses). The type of soap varied across studies but was predominantly bar soap.
6. Water (recurrent)	Expenditure on water used for handwashing, assumed to average 1.5 L/person/day (online supplemental material B).47