'~1' 与逻辑回归的含义

Question

这段代码中~1是什么意思

<块引用>

glm(credit.rating**~1**... scope=list(lower=~1...

step.logistic<-step(glm(credit.rating~1, data=train, family="binomial"),
                    scope=list(lower=~1, upper=~account.balance+credit.duration.months+previous.credit.payment.status+
                                 credit.purpose+credit.amount+savings+employment.duration+installment.rate+
                                 marital.status+guarantor+residence.duration+current.assets+age+other.credits+
                                 apartment.type+bank.credits+occupation+dependents+telephone+foreign.worker),
                    direction="both")