If you want to compare death rates in two cities with populations that have different age ranges, you should compare: crude death rates cause-specific death rates age adjusted death rates useful comparisons cannot be made between these two populations

representative sample

sociologists study the world, observe a predicament or interesting design, and set out to investigate it. they use investigation methods to design a study possibly a comprehensive, detailed and precise, by using experimental method for directing research and gathering data.

to study the characteristics of the whole population, sociologist prefers to obtain the sample which is the finite part of a demographic population whose characteristics are analyzed to obtain data from statistics.

when administering with population, it can be described as a set of respondents picked from a larger population for the goal of a survey. a population could be a group of objects, people, or articles from which samples are obtained for computation of the whole population which is the aim of the sociological study.

i guess the question is incomplete