Terms used for study designs:

Site comparison

A study that considers the effects of interventions by comparing sites that have historically had different interventions or levels of intervention.


The intervention was repeated on more than one individual or site. In conservation and ecology, the number of replicates is much smaller than it would be for medical trials (when thousands of individuals are often tested). If the replicates are sites, pragmatism dictates that between five and ten replicates is a reasonable amount of replication, although more would be preferable. We provide the number of replicates wherever possible, and describe a replicated trial as ‘small’ if the number of replicates is small relative to similar studies of its kind. In the case of reintroductions, replicates should be sites, not individuals.


Individuals or sites treated with the intervention are compared with control individuals or sites not treated with the intervention.


The intervention was allocated randomly to individuals or sites. This means that the initial condition of those given the intervention is less likely to bias the outcome.

Before-and-after trial

Monitoring of effects was carried out before and after the intervention was imposed.


A conventional review of literature. Generally, these have not used an agreed search protocol or quantitative assessments of the evidence.

Systematic review

A systematic review follows structured, predefined methods to comprehensively collate and synthesise existing evidence. It must weight or evaluate studies, in some way, according to the strength of evidence they offer (e.g. sample size and rigour of design). Environmental systematic reviews are available here.


If none of the above apply, for example a study measuring change over time in only one site
and only after an intervention. Or a study measuring use of nest boxes at one site.

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