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 NonPersistently 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 between x and yr 5 lna p 1 2 p

b. Minitab output resulting from fitting the least-squares line is given below.

The regression equation is ln(p/(1-p)) 20.917 2 0.107 Distance to Crop Edge Predictor Coef SE Coef T P Constant 0.9171 0.1249 7.34 0.000 Distance to Crop Edge 0.10716 0.01062 10.09 0.000 S 0.387646 R-Sq 72.8% R-Sq(adj) 72.1%

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.)