The margin effect bias in trend-surface models and its impact on the results of trend-surface analysis

Objective To explore the margin effect bias in trend-surface models and its impact on the results of trend-surface analysis.Methods By comparing with the trend contour plot of the same order trend -surface models between the benchmark surface and the special area of surveillance of disease in the benchmark surface,the impaction of margin effect bias to the result of trend-surface analysis was proved;and by setting up the buffer area around the special area of surveillance,the margin effect bias of trend-surface models in the special area of surveillance was controlled.Results When the order of the trend-surface model is bigger,the impaction of margin effect bias to the results of trend-surface analysis is stronger,setting up the buffer area around the special area of surveillance can control the impaction of margin effect bias effectively.Conclusion In order to controlling the margin effect bias,the buffer area around the special area of surveillance of disease would be set up,but when the buffer area could not be set up,the modeling of trend-surface analysis in the margin area should be carefully concluded.