2.4.2 Informant agreement ratio(IAR)
The use frequency was analyzed by the IAR which has been widely used in comparative ethnobotany(Trtter and Logan,1986;Heinrich et all.,1998;Leporatti and Ivancheva,2003;Collins et all.,Inta et all.2008) to measure the agreement between informants concerning what plants are used for specific use categories:
IAR=(Nur-Nt)/(Nur-1)
Where Nur is the number of use records in each use category and Not is the number of taxa used in each use category.IAR ranges from 0 to 1 and a value of 1 indicates that taxa are used by many informants,thus inferring a high degree of consensus and a well defined medicinal plant tradition (Heinrich et all.1998) For the purpose of this study, the taxon considered is species. IAR was calculated for each use category in each of the five studied Yuan villages.
2.4.3 Coefficient of determination (R)
Correlations between informants' age and number of medicinal plants uses by the Yuan were determined with the coefficient of determination (R) calculated by SPSS 11.0 for windows