Farm Table says:
Meta-analysis is a method for analysing and synthesizing the results of several independent studies examining the same question. is especially useful for examining general patterns of treatment effects, such as, for example, the evidence for interspecific competition in field experiments.
For simplicity, we used species richness as a quantitative index of biodiversity in our analysis, although it is only one of several measures of biodiversity.
• Abundance is the total number of individuals per unit area or, for many insects, per trap, or, for plants, percentage plant cover.
• Organic (sometimes called ecological) agriculture can be defined as farming systems where the use of pesticides, herbicides and chemical fertilizers is prohibited.
• Conventional agriculture encompasses farming systems where pesticides, herbicides and chemical fertilizers can be used.
The results show that organic farming often has positive effects on species richness and abundance, but that its effects are likely to differ between organism groups and landscapes. It is highly recommended that positive effects of organic farming on species richness can be expected in intensively managed agricultural landscapes, but not in small-scale landscapes comprising many other biotopes as well as agricultural fields. Measures to preserve and enhance biodiversity should be more landscape- and farm-specific than is presently the case.