Sustainability refers to the general phenomenon of the continuation of an intervention or its effects (Shediac-Rizkallah 1998, Swerissen 2004). Sustainability of interventions should be an important consideration in systematic reviews. Attention to the long-term viability of health interventions is likely to increase as policy makers, practitioners and funders become increasingly concerned with allocating scarce resources effectively and efficiently (Shediac-Rizkallah 1998). Users of reviews are interested in knowing whether the health benefits, such as reductions in specific diseases or improvements in health, are going to be sustained beyond the life of the interventions.
Unfortunately, collecting data on the extent to which the intervention and outcomes are sustained is often not carried out, which limits the extent to which long-term impacts can be assessed. Careful consideration in Cochrane reviews of how previous studies have (or have not) addressed issues of sustainability will increase our understanding in this area and hopefully also stimulate improved design for assessment of sustainability in future studies.
A sustained or sustainable program does not necessarily result in sustained outcomes and not all interventions need to be sustained in order to be useful or effective (Shediac-Rizkallah 1998). Also, review authors should consider whether the sustainability of the outcomes is relevant to the objectives of the intervention. If this is the case, authors should consider what outcomes have (or should have) been measured, over what period, and what the pattern of outcomes is over time.
Information should be sought on both contextual factors and intervention characteristics that may explain the extent to which the interventions or outcomes are sustained. Where sustainability of outcomes has not been measured, authors should explore the potential of the intervention outcomes to be sustained. Four frameworks may be useful to assist in determining sustainability:
Bossert lists the following five factors influencing sustainability (Bossert 1990):
the economic and political variables surrounding the implementation and evaluation of the intervention;
the strength of the institution implementing the intervention;
the full integration of activities into existing programs/services/curriculum/etc;
whether the program includes a strong training component (capacity building); and
community involvement/participation in the program.
The framework developed by Swerissen and Crisp (Swerissen 2004) guides decisions about the likely sustainability of interventions and effects at different levels of social organization. This framework outlines the relationships between intervention level, strategies and the likely sustainability of interventions and effects.
Shediac-Rizkallah and Bone present a useful framework for conceptualizing sustainability (Shediac-Rizkallah 1998). In this framework key aspects of program sustainability are defined as 1) maintenance of health benefits from the program; 2) institutionalization of a program within an organization; and 3) capacity building in the recipient community. Key factors influencing sustainability are defined as 1) factors in the broader environment; 2) factors within the organizational setting; and 3) project design and implementation factors.
The Centre for Health Promotion, University of Toronto, has also produced a document outlining four integrated components of sustainability (Health Communication Unit 2001).