What is selective surveillance?

When studying the properties of an object, the characteristic of not all the units of the general population is determined, but only of some of its parts. This makes it possible, by performing a selective observation of the selected region, to characterize quite adequately all the objects as a whole for some particular distinguished feature or property.

In order for the selected objects to be able to represent all the units under investigation with sufficient probability, the work must be organized in a certain way.

There are several traditional methods that make it possible to extend selective observation to the whole population, the main ones being the following: the method of coefficients and direct recalculation. The first option is used in cases where it is necessary to verify or refine data obtained as a result of continuous observation. In the second case, the product of the mean value of the test attribute is determined for the whole volume of the general population. In this case, it is necessary to take into account the fact that not all factors allow full use of a point estimate in the dissemination of results obtained for sampling the general population. Therefore, in practice, a fairly wide application of the interval estimation, with which one can take into account the size of the marginal error of a part of the population and calculate it for the average, and, if necessary, for the fraction of the trait.

When research is conducted not on the whole population, but only on its part, sampling errors that inevitably cause deviation of the results from true values can inevitably arise. At the same time, there are two main reasons that can cause distortion of the final result:

• Imperfection of the technical conditions of the study, the so-called registration error;
• Violation of the rules, which can be both random and systematic in the selection of units for research.

Selective observation in statistics is widely used. In this case, reliable information about the objects of research can be obtained, significantly saving money and reducing costs. The guarantee of the representativeness of the studies is the scientifically based selection of respondents for the study.

In practice, selective observation is most often performed at sites that have been selected in a random or zoned manner. In the first case, the same probability is ensured that one or another unit falls into the sample set. If the object of research after receiving information about it returns to the general population, then the random sample is called repeated. Otherwise it is repetitive. The zoned sample is formed as a result of the dismemberment of the general population into a number of regions (groups), depending on the character of the trait being studied. The use of suitable selection techniques makes it possible to ensure the presence of representatives from each group in the selected population.

If we talk about how a selective observation should be organized, then in this case it is necessary to observe the following conditions:

• The number of units in the sample should be maximum to ensure the detection of the desired patterns;
• It is necessary to adhere to the principle of equiprobable hit of each object in the sample;
• It is worthwhile to involve all parts of the studied population without exception.

This will allow you, by minimizing the volume of ongoing research, to obtain reliable information on the issues you are interested in.