Basic Survey Design
Surveys are used as a tool to collect information from some or all units of a population and compile the information into a useful form. There are two different types of surveys that can be used to collect information in different circumstances to satisfy differing needs. These are sample surveys and censuses.
In a sample survey, only part of the total population is approached for information on the topic under study. These data are then 'expanded' or 'weighted' to make inferences about the whole population. We define the sample as the set of observations taken from the population for the purpose of obtaining information about the population.
Disadvantages of Sample Surveys compared with Censuses:
Sample Survey Design Considerations
When running a sample survey, there are several design considerations that need to be taken into account that are specific to sample surveys. These additional factors include: sample size, sample design, the mode of estimation based on survey results and, where applicable, stratification, allocation of the sample across the strata and the selection of the sample within the strata. These factors, however, depend on many other factors such as the objectives of the survey, nature of target population, data items to be collected, level of accuracy required etc.
A census is a collection of information from all units in the population or a 'complete enumeration' of the population. We use a census when we want accurate information for many subdivisions of the population. Such a survey usually requires a very large sample size and often a census offers the best solution.
An examination of these shows that these closely reflect the disadvantages of a sample survey.
Similarly, the disadvantages of censuses relate to the advantages of sample surveys.
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