After Estimating a Probit Model for the Likelihood of a Website

Multiple Choice

After estimating a probit model for the likelihood of a website visitor clicking through conditional on the average income from the county in which the visit's IP address came from, you get the following results: ClickThrough_i = -1.8(0.75) + 0.06(0.005) Income_i, where standard errors are reported in parenthesis. What would be the calculation that yields the marginal effect of income moving from $40,000 to $41,000 on the click-through rate?

A) -1.8 + 0.06 = -1.74
B) Φ[0.06(41 - 40) ]
C) Φ(-1.8 + 0.06 × 41) - Φ(-1.8 + 0.06 × 40)
D) 0.8