## CHAPTER 9. Sample construction

To find out if the soup is salted, it is not necessary to eat the whole pan. One spoon is enough, but only if the soup mix well. This simple observation is based on the idea of ​​sampling. To get an idea of ​​the marketing characteristics of the population under study, it is not necessary to interview them all. You need to select a relatively small number of them, but select it correctly. At the same time, the correctness of sampling means the selection of objects in a random way, and so that each member of the population under investigation has not necessarily equal but necessarily known to the researcher and a non-zero probability to be selected.

## 9.1. The concept of sampling. Advantages and disadvantages of the sampling method in comparison with the full census

The goal of most marketing projects is to evaluate the characteristics of that or other set elements (the population under investigation). Such a characteristic - for example, the proportion of consumers who prefer a certain brand of toothpaste. Identify these characteristics can be both based on a complete census (census), and based on the sample (sample). Complete census means obtaining information about each of the elements of the population under study. Census allows you to directly calculate searched values. The sample involves obtaining information not only about everyone, but only about some elements selected for participation in the study. Sampling-based, selective values ​​ for or statistics are approximate estimates of their true values ​​ on all elements of the population under study. In this case, procedures for estimating and testing hypotheses are used.

However, whatever evaluation procedures are applied, there is always a sampling error-the discrepancy between the sample characteristics and the characteristics of the population under study. Therefore, in some cases it is better to conduct a full census rather than a sample survey.

First of all, it can be situations where the number of elements of the studied population is not too large. For example, if it is not a consumer product, but a product of industrial purpose, when it is possible to sort through all the enterprises that are already or can become buyers of the products of interest to us. An example of such a situation is Finding out the share of the UK market for chemicals for paper production (see pages 17, 160, 275).

The full census is also preferable when the random sampling error is relatively large (see page 179), for example, because one part of the objects of the population under study is very different from the other. So, the results of a survey of potential equipment buyers may depend on whether or not they got into the sample of the company "Forda". After all, it is known that approaches to the selection of equipment at Ford enterprises and, say, Honda are completely different.

On the other hand, the very fact of carrying out a complete census leads to an increase in errors not related to sampling (for example, to deliberate distortion of information by respondents during the interview). As already noted, the size of such errors is often significantly higher than the errors associated with the sample. If errors that are not related to sampling are relatively large, selective research is preferable. This is one of the reasons why the results of some censuses have to be checked by conducting selective studies.

Moreover, it is not uncommon for the very fact of the conduct and content of research to be kept, as far as possible, from competitors by secret. Here, a complete census, of course, is unacceptable.

Last but not least, selective research is usually much cheaper and, in addition, faster.

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