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Exercise

binomial family argument

The big difference between running a linear regression with lm() and running a logistic regression with glm() is that you have to set glm()'s family argument to binomial. binomial() is a function that returns a list of other functions that tell glm() how to perform calculations in the regression. The two most interesting functions are linkinv and linkfun, which are used for transforming variables from the whole number line (minus infinity to infinity) to probabilities (zero to one) and back again.

A vector of values, x, and a vector of probabilities, p, are available.

Instructions

100 XP
  • Examine the structure of the binomial() function. Notice that it contains two elements that are functions, binomial()$linkinv, and binomial()$linkfun.
  • Call binomial()$linkinv() on x, assigning to linkinv_x.
  • Check that linkinv_x and plogis() of x give the same results with all.equal().
  • Call binomial()$linkfun() on p, assigning to linkfun_p.
  • Check that linkfun_p and qlogis() of p give the same results.