Which of the following is false with regard to prevalence ?

Prevalence: Prevalence is defined as  "the total number of all individuals  who  have an attribute or disease at a  particular time  (or  during  a particular  period)  divided  by  the population at risk  of having the attribute or disease at this point in time or midway through the  period.  Although referred to as a rate, prevalence rate is really a ratio.  Prevalence is of two types :          (a) Point prevalence          (b) Period prevalence  When  the  term  "prevalence  rate"  is  used,  without any  further  qualification,  it  is  taken  to  mean  "point prevalence".