In a study of 43 blind individuals (with no eyesight), a grooved surface was pressed against the index finger of each of the individuals. An individual€™s threshold was defined to be the smallest distance between grooves in which the individual could correctly identify the grooves as being horizontal or vertical. The test was first done by applying 10 g of pressure and then done by applying 50 g of pressure. The scatterplot and the model in Fig. 131 compare the 10-g thresholds with the 50-g thresholds of the individuals, both in mm.

Let x be an individual€™s 10-g threshold, and let y be the in-dividual€™s 50-g threshold, both in mm. The equation of the model shown in Fig. 131 is f (x) = 0.86x - 0.16.
a. Is the association positive, negative, or neither? What does that mean in this situation?
b. Find f(1.5) Which is larger, 1.5 or f(1.5)? What does your comparison mean in this situation?
c. Find f(2) Which is larger, 2 or f(2)? What does your com- parison mean in this situation?
d. Find f(3) Which is larger, 3 or f(3)? What does your com- parison mean in this situation?
e. On the scatterplot, imagine the line y = x. Or use a strand of thread, a stretched rubber band, or the edge of a clear ruler to form the line. Do most of the data points lie below, on, or above the line? What does that mean in this situation?

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10-g Threshold versus 50-g Threshold 2.5 1.5 ·:/뎐 0.5 0.5 15 2 25 3 10-g threshold (mm)