Evidence is strong when we have confidence that additional data will not reverse our conclusions. This is generally the case where there are consistent findings across multiple studies or where the magnitude of effects are very large. Studies where rigorous experimental designs are used (including before-comparisons as well as an appropriate control group) also generate confidence. Although there is not yet consensus among conservation practitioners around a particular formula for evidence grading at this time, expert judgment should consider these factors when assessing strength of evidence.