A point prevalence rate is strictly not a rate as no time period is involved
The risk of an event is the total number of events in the period of interest divided by the total number of years (or relevant unit of time) of follow-up for all individuals.
A rate cannot be calculated in a longitudinal study.
The relative rate is equal to the difference in two rates
The relative rate of a disease can be taken as an estimate of the relative risk if the prevalence of the disease is high