The multiplier method is a method to estimate population size (e.g. the number of sex-workers in a city), popular among epidemiologists. However, it relies on the identity that p_t = N_t/N, where p_t is the proportion of target population with a certain trait, N_t is the number of people with this trait, and N is the size of the target population. This causes problems in today's world where information on many traits exist in record such that each trait can be used to generate an estimate. I will introduce a recent extension of the multiplier method with which information on multiple traits are used simultaneously to produce a single estimate of population size. I will include examples and some theoretical findings on the effect of study design on inference precision.