Explain statistical indicators method.

The concept of index occurred at the beginning of the century XVIII century, with the study undertaken by the Anglican Bishop W. Fleetwood (Chronicon Preciosum, London, second edition, 1745) on the evolution of prices in England between 1400 and 1700, aimed to show whether a clause of the college, established three centuries ago, will retain its validity still, taking into account the price evolution.For this purpose, he took into account four current consumer products: wheat, meat, drink and clothes, researching the evolution of prices over time, reaching the following conclusion: £ 5 in the period 1440-1460 could buy as many consumer products (from the chosen by him) as with £ 30 in 1700.

Indices represents a category of statistical indicators by which to measure the variation in average relative social and economic phenomena in time and space or in relation to another level, considered as the basic or standard.
By definition, any index is obtained by reporting between two absolute levels of the same phenomenon or group of phenomena. One is the volume levels of the phenomenon considered as a basis for reporting. . The level chosen as the basis for comparison should be a normal level of development of the phenomenon investigated, a level that has a special meaning (to represent a particular step or stage of development), so as to justify the choice of standard statistical analysis .

Statistics index method is used to characterize the average relative variation of phenomena over time, to compare events in their area, to measure the influence of different factors on the level and structure of complex phenomena.

In theory and practice  various statistical indices are used, which differ among themselves in multiple ways. Therefore, to form a coherent picture on them is required to be classified in several ways:

1) in terms of coverage area, indicators are divided into two categories:
▪   individual or simple / basic indices, measuring the relative variation of these simple phenomena , single in time or space;
▪ group indices compounds / synthetic, measuring average relative variation of collective phenomena in relation to some basis for comparison.

2) the nature of the feature studied, there are two categories of indices:
▪ indices of change over time or growth indices;
▪ indices of change in space or territorial indices.

3) Depending on the mode of election of the reporting period, both indices  individual and the compounds are divided into:
▪ indices with fixed base;
▪ indices based furniture.

4) in terms of weights used, particularly:
▪ indices with constant weights;
▪ indices with variable weights.

5) in terms of the calculation process, the group indices are divided into:
▪ aggregate indices;
▪ indices calculated as weighted arithmetic averages of individual indices;
▪ indices calculated as the weighted harmonic average of individual indices
▪ indices calculated as the geometric average;
▪ indices calculated by reporting a second weighted arithmetic average, etc.