We will first discuss the direct method of adjusting rates.
Direct adjustment of rates requires a standard population,
to which the estimated age-specific rates for the population
under evaluation can be applied. This standard can represent
the combination of the two populations being compared, or a
standard that reflects, for example, the US or the world
population. The choice of the standard population is somewhat
arbitrary. Although it may affect the magnitude of the
age-adjusted rates, the choice of the standard will not affect
the ranking of the population being compared.