[R] Inverse of Probit
bbolker at gmail.com
Wed Nov 20 22:49:13 CET 2013
David Winsemius <dwinsemius <at> comcast.net> writes:
> On Nov 19, 2013, at 10:59 AM, Calum wrote:
> > Hi there,
> > I hope someone can help me.
> > I have a dataset of Concentration against Mortality, and I am trying to
> > compare the use of Logit and Probit models using this data.
[snip snip snip]
There are three ways you can get the inverse-link function
1. dig into the family object: binomial(link="probit")$linkinv
2. know that the probit link is the qnorm() (Normal quantile) function,
and the inverse-probit is pnorm() (the Normal CDF). (Similarly, it
seems that a lot of users don't know that plogis()/qlogis() similarly
provide the logistic and logit functions ...
3. As David Winsemius suggests, use predict(...,type="response")
(but options #1 and #2 are useful in providing flexibility).
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