Analysis of influencing factors on water iodine in Shandong Province based on geographically weighted regression / 中华地方病学杂志

ABSTRACT

Objective To analyze the influencing factors of water iodine in Shandong Province.Methods The county-based study set Shandong Province as a research site.The water iodine data of county (city) from 2008 to 2010 were obtained from Shandong Institute for Prevention and Control of Endemic Disease.Water iodine content was used as a dependent variable,and soil type,hydrogeological type,topography and distance to the Yellow River were analyzed as independent variables.Normality test and general linear regression analysis of the dependent variables were performed using SAS 9.3 software;geographically weighted regression (GWR) analysis was performed using SAM V4.0 software;related electronic maps were drawn using ArcGIS 9.3 software.Results A total of 108 164 water iodine content data were collected.General linear regression analysis showed that the constructed regression model was statistically significant (F =16.29,P ＜ 0.01),and the soil type was included in the model with a determination coefficient (R2) =0.51.GWR analysis showed that R2 =0.63 and the adjustive determination coefficient (R2adj) =0.59.Considering the autocorrelation of the variable space,the model's goodness of fit was better than that of the traditional general linear regression model.GWR analysis showed that soil type and distance to the Yellow River were major factors related to water iodine in Shandong Province.There was a negative correlation between soil type and spatial variability of water iodine in most areas of Shandong Province,the correlation coefficients weakened gradually from west to east,indicating a geographic gradient variability.The correlation coefficients of distance to the Yellow River and spatial variability of water iodine were negative in some areas,while they were positive in other areas,indicating a clear geographical variability from southwest to northwest.Conclusion The soil type and the distance to Yellow River are important factors affecting the spatial distribution of water iodine in Shandong Province.