List any four characters that are employed in human population census.

(N/A) The four key characters employed in human population census are:
$(i)$ Birth rates (Natality): The number of births per unit of population per unit time.
$(ii)$ Death rates (Mortality): The number of deaths per unit of population per unit time.
$(iii)$ Sex ratio: The ratio of the number of females to the number of males in the population.
$(iv)$ Age distribution: The percentage of individuals of a given age or age group in the population.