Organising evidence for environmental decisions

This blog was created as part of the original Valuing Nature Network (2011-2014)

Today colleagues and I published a paper that brings together years of thinking and discussion about how to provide environmental managers access to the best available scientific evidence (Dicks et al. 2014). The mainstay of our approach is a ‘4S’ hierarchy.

This describes different levels of evidence synthesis, each level more condensed and accessible to decision-makers than the level below. The four Ss are: Studies, Systematic Reviews, Summaries, and Decision Support Systems. OK, we know that the last one’s really a D. 

The idea is not ours. It was devised by people working on evidence for medicine and public health, who have been using synthesized evidence to inform clinical and policy decisions for decades. 

You can read a description of the 4S hierarchy here: . The paper is free to download. It includes definitions, guidance and costs for developing each level of evidence synthesis, and a diagram showing how synthesized evidence relates to environmental decisions. 

Two things are important about the 4S framework. First, it minimises bias. Second, it encourages transparency. Biased views of existing evidence are very easy to paint, even using apparently rigorous academic review papers. Look at the fierce debates that rage over the impact of neonicotinoids on bees, for instance. You can use scientific review papers to make a case on either side of that argument (compare, for example, Goulson, 2013 with Godfray et al. 2014). 

The second level of the 4S hierarchy, above individual studies (science’s raw data), comprises systematic reviews, as published by the Collaboration for Environmental Evidence, or, for medicine, the Cochrane Collaboration. Have a look at the process required to publish a systematic review. You will be amazed how much care is taken to avoid bias, and to include only evidence of acceptable scientific quality. For one thing, your search terms and selection criteria have to be peer-reviewed before you conduct the search. The upper levels of evidence synthesis in the 4S hierarchy refer back to systematic reviews and incorporate those that are available.  

On transparency, the 4S framework helps to clarify where evidence is coming from, by naming the different sources of evidence. This approach is already being used by the New Zealand Department of Conservation to help them improve how they use evidence. We identify a number of common bypass routes – guidance based on a small subset of studies for example, or decision support systems relying on an incomplete scientific understanding. Often these are necessary, to allow decisions to be made in time. 

Building a complete 4S hierarchy for all environmental issues is no small undertaking. The Collaboration for Environmental Evidence and the Conservation Evidence project are making substantial progress, but there is a long way to go.  If a greater proportion of the millions of dollars spent globally each year improving ‘science-policy’ interactions and reviewing science (again) for individual policy questions were diverted to building the 4S hierarchy, we could get there a lot faster. 


Dicks, L.V., Walsh, J.C. and Sutherland, W.J. (2014) Organising evidence for environmental management decisions: a ‘4S’ hierarchy. Trends in Ecology and Evolution. Online early.

Goulson, D. (2013), REVIEW: An overview of the environmental risks posed by neonicotinoid insecticides. Journal of Applied Ecology, 50: 977–987. doi: 10.1111/1365-2664.12111

Godfray H.C.J., Blacquie`re T., Field L.M., Hails R.S., Petrokofsky G., Potts S.G., Raine N.E., Vanbergen A.J., McLean A.R. (2014) A restatement of the natural science evidence base concerning neonicotinoid insecticides and insect pollinators. Proc. R. Soc. B 281:20140558.