Tuesday, 1 May 2012


Q3. A. Differentiate between ‘Census survey’ and ‘ Sample Survey’. b. Analyze multi-stage and sequential sampling. [5 Marks]

Surveys are done all over the world to collect information from the populace to arrive at conclusions that help in improving the products or services of a company. There are many techniques of survey out of which sample survey and census survey are very popular. Though there are many similarities between these two methods, there are many differences in features and also the results obtained.
It depends upon time available and other circumstances to engage in either of the two types of surveys. This article will discuss the features of two types of surveys to clear the doubts in the minds of the readers.

Before we begin to differentiate, it is pertinent to note that sample is a portion of the population whereas census takes into consideration everyone in the population. This obviously means that a census survey is a much bigger exercise in nature and procedures than a sample survey. Census survey also is a very time consuming exercise as information needs to be collected from each and every individual from the population. On the other hand, sample survey is easier as a representative sample is taken from the population and the results obtained are extrapolated to fit the entire population.

There are times and requirements where governments have to indulge in census survey even if it is time consuming and very expensive as it needs to formulate policies and welfare programs for the population. For example, when a government has to count heads of the population, it cannot conduct a sample survey to count the number of people in the country. But when government is planning on a welfare program for cancer patients, it can conduct a sample survey of some of the cancer patients and then extrapolate the results on the section of the population that is undergoing treatment for cancer.

There are errors in sampling in case of sample survey which can be minimized but never eliminated. Therefore the results of a sample survey always have a margin for error whereas census survey is always accurate. However, many times, it is not possible to carry out census survey which is when sample survey is undertaken.

b. In multi-stage sampling method, sampling is carried out in two or more stages. The population is regarded as being composed of a number of second stage units and so forth. That is, at each stage, a sampling unit is a cluster of the sampling units of the subsequent stage. First, a sample of the first stage sampling units is drawn, then from each of the selected first stage sampling unit, a sample of the second stage sampling units is drawn. The procedure continues down to the final sampling units or population elements. Appropriate random sampling method is adopted at each stage. It is appropriate where the population is scattered over a wider geographical area and no frame or list is available for sampling. It is also useful when a survey has to be made within a limited time and cost budget. The major disadvantage is that the procedure of estimating sampling error and cost advantage is complicated.

Double sampling refers to the subsection of the final sample form a pre-selected larger sample that provided information for improving the final selection. When the procedure is extended to more than two phases of selection, it is then, called multi-phase sampling. This is also known as sequential sampling, as sub-sampling is done from a main sample in phases. Double sampling or multiphase sampling is a compromise solution for a dilemma posed by undesirable extremes. “The statistics based on the sample of ‘n’ can be improved by using ancillary information from a wide base: but this is too costly to obtain from the entire population of N elements. Instead, information is obtained from a larger preliminary sample nil which includes the final sample n.

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