The dataset Crabs2.dat at the text website collects several variables that may be associated with y = whether a female horseshoe crab is monandrous

(eggs fertilized by a single male crab) or polyandrous (eggs fertilized by multiple males). A probit model that uses as explanatory variables Fcolor =

the female crab’s color (1 = dark, 3 = medium, 5 = light) and Fsurf = her surface condition (values 1, 2, 3, 4, 5 with lower values representing worse)

has the output shown. Interpret the parameter estimates and the inferential results. Approximately what values would you expect for the ML estimate of the Fsurf effect and its SE if you fitted the corresponding logistic model?

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Estimate Std. Error z value Pr(>|z|)

(Intercept) -0.3378 0.1217 -2.775 0.005522 factor(Fcolor)3 0.4797 0.1065 4.504 6.66e-06 factor(Fcolor)5 0.1651 0.1158 1.426 0.153902 Fsurf -0.1360 0.0376 -3.619 0.000296

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Null deviance: 1633.8 on 1344 degrees of freedom Residual deviance: 1587.8 on 1341 degrees of freedom

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