Standardization of rates in Demography is required for comparison of various rates concerning human population either between different groups or the same group over a period of time requires careful thinking. One of the most important problems in demography is comparison of rates and ratios among different populations or for the same population over time. Such comparisons are essential for an understanding of underlying factors contributing to demographic differences between populations and in the same population over time. If one place has a higher crude death rate (CDR) or a disease specific morbidity rate as compared to another place, it does not necessarily mean that the condition of general mortality or the prevalence of the particular disease in the place with higher rates is higher than the other place. It is known that the mortality conditions as well as the incidence of most of the diseases vary from age group to age group as well as from sex to sex. It is quite evident that the age specific death rates in lower age groups and upper age groups are higher as compare to middle age groups. As an example, when observations are made in a community with higher proportions of middle aged people and compared with a community with large proportions of other age groups, it is obvious that the CDR of the former to be less than the CDR of the latter. This difference in the CDR between the two communities may be mainly because of the differences in the age structure of the two communities and may not be because of the differences in the mortality conditions. Similarly, in addition to age structure, the sex structure will also play a role in bringing about the differences in the CDR between the two communities.
Hence in order to compare either the mortality conditions or disease conditions between places or over a period of time, the Standardization of rates needs to be done with reference to age and sex groups and then comparisons are to be made. That is to say that the overall rates for the communities are to be calculated after giving due weights for the age and sex structure of the community as well as the age and sex specific rates of the event under study. Then only overall comparisons will yield correct picture.