Some plant viruses are spread by insects and tend to spread from the edges of a field inward. The data on x 5 distance from the edge of the field (in meters) and y 5 proportion of plants with virus symptoms that appeared in the paper “Patterns of Spread of Two Non-

Persistently Aphid-Borne Viruses in Lupin Stands” (Annals of Applied Biology [2005]: 337–350) was used to fit a least-squares regression line to describe the relationship

a. What is the logistic regression function relating x and the proportion of plants with virus symptoms?

b. What would you predict for the proportion of plants with virus symptoms at a distance of 15 meters from the edge of the field? (Note: the x values in the data set ranged from 0 to 20.)

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between x and y = In(). Minitab output re- sulting from fitting the least-squares line is given below. The regression equation is In(p/(1-p)) = -0.917 -0.107 Distance to Crop Edge Predictor Constant Coef SE Coef T P -0.9171 0.1249 -7.34 0.000 -10.09 0.000 Distance to Crop Edge -0.10716 0.01062 S=0.387646 R-Sq = 72.8% R-Sq(adj) = 72.1%