The problem of comparability of levels of time series Jointing (смыкание) of time series
Since time series is formed during the long period of time, its levels are frequently incomparable
Reasons of the incomparability 1.Change of prices. 2.Different methods of calculation of the same indicator. 3.Change of «borders» (organizational, administrative)
The method of jointing time series is often used to ensure the comparability of data. It is necessary to have a transitional link (переходное звено) for jointing time series. Transitional link – is the period of time, for which the investigated indicator was calculated using the old method (in old borders) and the new method (in new borders). A transitional coefficient for this transitional is calculated, the transitional coefficient spreads over all the previous period of time
Analysis of the main tendency of time series
The levels of time series are formed under the influence of lots of factors. They can be divided into 5 groups
Time-Series Components Time Series Cyclical Compo- nent Irregular Compo- nent Trend Compo- nent Seasonality Component Secular Compo- nent
1. Determining ( Определяющие) factors have a constant and strong influence on the examined indicator. They determine the main tendency (the trend) of time series
There are 4 kinds of charge or variations involved in time series analysis. They are: 2.Secular trend U t. In the secular trends the value of variable tends to increase or decrease over a long period of time. The steady increase of the cost of living recorded by the Сonsumer price index is an example of secular trend. From year to year, the cost of living varies a great deal, but if we examine long-period, we see that the trend is toward a steady increase.
3. Cyclical fluctuation V t. The most common example of cyclical fluctuation is the business cycle. Over time, there are years when the business cycle hits a peak above the trend line. At other times, business activity is likely to slump, hitting a low point below the trend line. The time between hitting peaks and falling to low points is at least one year and it can be as many as 15 or 20 years.
4. Seasonal variation S t involves pattern of change within year that tend to be repeated from year to year. For example the consumption of drinks, juices, ice cream and other. Seasonal factors give rise to oscillations relative to the main tendency