Relevant evidence

Are the subjects very different?

Always ask yourself if the intervention comparisons included only subjects (e.g. crops, livestock, farms) that are very different to the ones that you are interested in.

Farming systems can differ to each other in many ways. Most of the time when there are intervention comparisons only in one type of farming system or region, it is very uncertain what the effects of the interventions are in other situations. For example, farmland research is often carried out in Western Europe or in North America, and these environments may be very different to tropical or dryland environments for example. Similarly, the effectiveness of interventions may vary in different breeds of livestock or varieties of crop there may only be comparisons in a limited range of these.

REMEMBER: Ask whether your situation is very different from those used in fair comparisons of interventions.