# Risk ratios in a Cox hazard model

I'm reading a paper which gives "Risk ratios from Cox hazard models with time-varying covariates".

Time-varying covariates just means that, for example if $X_i$ is a covariate for person $i$ then it might be $0$ at some time and $1$ at another time.

I understand that we can specify this model by saying that the $i$-th person's hazard rate at time t, for the decrement we're interested in, is:

$$\lambda_i(t) = \lambda_0(t)e^{\beta X_i(t)}$$

(i.e. there is only one covariate in the model)

In this case, the hazard ratio is $e^{\beta X_i(t)}$ but it's not clear to me what the author means by giving a risk ratio.

Can anyone help?