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The purpose of a sample survey is to make inferences about certain characteristics of a population from which samples are drawn. The inferences to be made for a population usually entails the estimation of population parameters, such as the population total, the mean, or the population proportion of a certain characteristic of interest. In any sample survey, a clear statement of its objective is very important. Without a clear statement about the objectives, it is very easy to miss pertinent information while planning the survey that can cause difficulties at the end of the study.

In any sample survey, only relevant information should be collected. Sometimes trying to collect too much information may become very confusing and consequently hinder the determination of the final goal. Moreover, collecting information in sample surveys costs money, so that the interested party must determine which and how much information should be obtained. For example, it is important to describe how much precision in the final results is desired. Too little information may prevent obtaining good estimates with desired precision, while too much information may not be needed and may unnecessarily cost too much money. One way to avoid such problems is to select an appropriate method of sampling the population. In other words, the sample survey needs to be appropriately designed. A brief discussion of such designs is given in Chapter 2. For more details on these designs, the reader may refer to Cochran (1977), Sukhatme and Sukhatme (1970), or Scheaffer et al. (2006).