Some genes tend to increase a given characteristic, and others work to decrease that same characteristic. The complex relationship among the various genes, as well as a variety of random factors, produces the final outcome. Furthermore, genetic factors always work with environmental factors to create personality. Based on this concept, gene–environment interaction can be defined as “a different effect of an environmental exposure on disease risk in persons with different genotypes,” or, equivalently, “a different effect of a genotype on disease risk in persons with different environmental exposures.”