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Chained unit value indexes of Galicia, the Basque Country and the
Murcia Region. Methodological document.
1. Introduction
Commercial foreign trade is an indicator of the increasingly greater openness of developed
economies, as can be seen from the monthly information on Foreign Trade Statistics provided by
the Spanish Tax Office.
Between 2000 and 2008, Spain’s total imports grew by nearly 70% while exports were up by over
50% during the same period. If we look at the foreign trade of the Autonomous Communities of
Galicia, the Basque Country and the Murcia region, this growth was still higher, as the aggregate
of the three Autonomous Communities doubled imports and a 70% growth in exports was
recorded. As a result of the great growth in imports, the foreign trade balance which was
practically null in 2000, came to nearly six thousand million euros in 2008, which accounted for
3.8% of the GDP of the three autonomous communities.
Special mention should be made of the significant growth in the imports of the Murcia Region,
which was up by 155% over the eight years in question, followed by the Basque Country that
nearly doubled its total imports, while Galicia registered growth slightly over the national level, at
74%. With respect to exports, the Autonomous Community that registered greatest growth was
Galicia with nearly 90% and it is the only of the economic territories included in the study where
the growth of the exports was higher than that of the imports. In the Basque Country, exports were
up by nearly 70%, while their growth in the Murcia Region was slightly over 40%.
Nonetheless, the weight of the foreign trade of the three autonomous communities is uneven. The
value of the total goods traded abroad in 2008 in the Murcia Region accounted for 3.2% of the
national total, which stood at 6.6% in Galicia and 8.5% in the Basque Country.
This uneven weight of the foreign trade of the three autonomous communities is related with the
also uneven weight of its economies, and it is therefore clearer to relate it with the Gross Domestic
Product (GDP) by calculating the opening-up rate. The three opening-up rates had similar values,
and stood at 53% in the Murcia Region, 55% in Galicia and 58% in the Basque Country in 2008.
For the Spanish economy as a whole, in the same year, the opening-up rate is 43%, which
indicates that these three economies are more open to other countries than the national average.
Foreign Trade Statistics has the Single Administrative Document (S.A.D) and the INTRASTAT
system used for collecting statistics on the trade in goods between countries of the European
Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Union as source of information. It allows us to establish the commercial flows of the companies of
different countries, including in the case of Spain, information on the Autonomous Community
which is the origin or destination of each commercial flow.
It is therefore information based on records, which provide highly relevant information about the
statistical value and the amount traded in each operation, which converts these records into an
important source of information on the prices of those operations at a low cost, as it means that
surveys do not have to be conducted with export and import companies.
The indexes that are prepared based on this information are the foreign trade Unit Value Indexes
(IVU) and provide an approach to the real price indexes of the operations to import and export
goods.
It is an approach to the prices of foreign trade operations, as the prices to which they refer are not
perfectly differentiated individual goods, but rather more or less uniform sets of classes of goods.
The main characteristics of the IVUs are:
a) They can be used to approximate the trend of the import and export prices
b) They are used as deflators for foreign trade in constant euros.
c) They are used to construct important indicators such as the real trade ratio or competitiveness
indexes.
The Ministry for the Economy and the Treasury has obtained the IVUs for the Spanish economy
since 1968, while at Autonomous Community level, special mention should be made of the
indicators obtained by the Galician Statistics Office (IGE) since 2000 and the Andalusian Statistics
Office (IEA) since 2003.
The IGE has performed a change of base of its IVUs in 2007 and used the opportunity to adapt
the methodology used to the reality of changing trade with new products constantly entering and
leaving. Furthermore, the calculation formulas recommended by Eurostat are applied in the new
2005 base, together with the chained indexes based on the Fisher formula. These formulas are
applicable to the IVUs as the latter are calculated based on records that contain all the goods
traded, while other price indexes (IPC, IPRI), which must be based on a sample of goods, which
would be very expensive to modify every year.
In 2008, the Murcia Regional Statistics Centre (CREM) and the Basque Statistics Office
(EUSTAT) considered the need to obtain an indicator of the prices of the foreign trade operations
in their respective autonomous communities. The fact that these indicators had already been
estimated in an Autonomous Community and the suitability of its methodology led both entities to
choose the methodology that was already being applied by the IGE. They received the support
and help of the technicians in charge of the same operations in Galicia. This meant that price
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
indicators of foreign trade operations in three perfectly comparable autonomous communities
could be obtained at a low cost and they are therefore discussed jointly in this publication.
2. Main methodological aspects
The chained unit value indexes (IVU) are based on the annual selection of uniform product groups
known as elementary classes from which unit values are obtained (as an approach to the prices).
Year-on-year comparisons are performed using the unit values of these elementary classes and
they are then chained to obtained indexes.
Schematically, the indexes are calculated using the following process:
2.1 Processing the base statistical information.
2.2 Defining the elementary classes.
2.3 Calculating the unit values of the elementary classes.
2.4 Selecting elementary classes.
2.5 Calculating the simple indexes of the elementary classes.
2.6 Designing the aggregation mechanism to build composite indexes.
2.7 Calculating the aggregate IVUs by usage groups.
2.8 Processing the non-selected elementary classes.
2.9 Debugging.
This document sets out the main methodological aspects of the IVUs obtained by the IGE,
EUSTAT and CREM and the specific characteristics of each one of them. For further details used
and specifically, all the mathematical formulas of the indexes, classifications and correspondences
used, please consult the methodologies available from the three statistical entities.
2.1 Processing the base statistical information.
As has already been indicated, the base statistical information comes from the administrative
records of the Customs and Special Levies Department of the Spanish Tax Office, which every
month collects the foreign trade operations of goods that occur in Spain, indicating the
Autonomous Community that is the origin or destination of those international flows. The data are
directly downloaded from the Spanish Tax Office’s website.
In order to calculate the unit value indexes, the information of interest is: the flow (export or
imports), the origin or destination country, the product (classified by Combined Nomenclature (NC)
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
or the Integrated Tariff of the European Communities (TARIC) codes, the value of the operation,
the weight, the number of traded units of the goods and the province of origin or destination.
The “province of origin/destination" of the Customs Department data is used to allocate the
province, except when this field appears without a value, in which the province is allocated
according to the "fiscal domicile province of the exporter/importer" variable.
Those products whose prices are not in line with the general trend, such as jewels or works of art,
were excluded from the base information. Vessels and aircraft were also eliminated as their
presence is not guaranteed every month and as their potential high value greatly distort the series.
The excluded products are the following groups of the CUCI classification: 667, 792, 793, 811,
896, 897, 899, 911, 931, 961, 971.
In the IVUs of the Basque Country, in addition to the aforementioned products, trains, which are in
group 791 of the CUCI, are not included when calculating the indexes, to avoid any distortion that
that may cause to the series.
When designing the IVUs of the Murcia Region, the oil imports needed to processed in a special
way. In 2000, the imports of this Autonomous Community doubled, due to the oil imports for the oil
pipeline that was opened between the Cartagena and Puertollano refineries that year. In order to
avoid the impact of these imports, which are allocated to the Murcia Region in the Foreign Trade
statistics but which according to the European Accounts System, SEC95 (3.133) must be
considered as import of the Autonomous Community of Castilla-la Macha, corrector coefficient
have been applied since that year to the imports of products included in the CUCI 333.
2.2 Defining the elementary classes.
The elementary classes are made up of product groups for which the unit values are calculated at
the greatest level of desegregation.
On the one hand, it is desirable to have the most desegregated classes to ensure their uniformity,
but on the other hand, the variety of situations, the reduced sample size which we face when
analysing a smaller autonomous community (when not directly the lack of observations) and the
possible existence of errors, encourages the consideration of wider classes.
The elementary classes are defined using the intersection of the five following characteristics:
1. Flow:
A difference is made between imports and exports.
2. Geographical zone:
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Given that the foreign trade data must be divided due to the geographical desegregation, the
following desegregation is carried out:
1. Euro zone countries (EMU Area)
2. European Union countries that do not belong to the EMU Area (EU Area)
3.
OECD countries that do not belong to the EU area (OECD Area)
4. Other countries (RM Area).
The IVUs of Galicia and the Basque Country consider these four geographical zones to define
their elementary classes, while the smaller size of the Murcia Region meant that it was advisable
to consider only three zones, by considering the EU countries overall and without distinguishing
whether or not they belong to the euro zone.
The IVUs of Galicia took into account the 25 countries making up the EU on the 1st January 2005,
while the 27 countries that currently make up this economic area were considered in the Murcia
Region and the Basque Country. Nonetheless, the small weight, 0.4% of the total, of the
commercial trade between Galicia and Rumania and Bulgaria means that the EU IVUs of the three
autonomous communities may be compared without significant errors.
3. CUCI Classification:
The elementary classes are defined using the CUCI groups (International Trade Unified
Classification). The CUCI regroups the TARIC classification (which was originally used to classify
the data) in categories according to the materials used, the preparation stage and the final use.
This classification is used to three digits.
4. Usage Group (UG):
This is a classification criterion based on the requirements of the Economic Accounts Systems
(SEC) and prepared by the General Sub-Directorate of Macroeconomic Analysis (SGAM) of the
Ministry of the Economy and the Treasury and the Spanish Statistics Institute (INE). This
classification is used to four digits, which takes a total of 28 different groups, to define the
elementary classes.
5. Unit type:
It was decided to consider the unit type in which the operation is measured as an additional
criteria to define the elementary class. Therefore, if two products are measured in different units,
they will belong to two different elementary classes, even though they are assigned to the same
GU and to the same CUCI.
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Therefore, the initial elementary classes are obtained using all the intersections that can occur
between the trade flow, geographical zone, GU to four digits, CUCI groups and unit types, even
though it must be taken into account, for example, that not all the unit types can occur in all CUCI
groups when determining the real number of possible classes. The CU and CUCI variables are
obtained using the correspondence between these classifications and the TARIC, which is the
product classification used in foreign trade.
2.3 Calculating the unit values of the elementary classes.
The unit value of an elementary class in a specific month is calculated as the weighted average of
the prices of the operations belonging to that class. The weighting reflects the relative importance
of the amount trade in each operation with respect to the total operations in said month.
The main drawback of using unit values is the composition effect, which may appear when the
relative structure of the trade is modified within the group where the unit value is calculated. In
these cases, the unit value may vary as the structure of the articles include in an elementary class
was altered, even though the prices of said articles are not modified.
2.4 Selecting the elementary classes.
The base statistics information does not guarantee that a representative unit value can be
calculated for the total operations carried out for all the elementary classes observed. Therefore,
once the unit values of all the elementary classes are obtained, a method to select elementary
classes needs to be designed so that we can effectively estimate unit values in a reliable manner,
and a procedure to process the elementary classes that were not selected.
As far as the problems that prevent the reliable estimation of unit values and which condition the
processing to be given to all the classes are concerned, we can group them into two:
1) The problem of the sample size:
It refers to the need to have a minimum number of monthly observations of the elementary class
to be able to calculate the relevant IVU in a regular manner. Given that the IVUs are calculated
for three autonomous communities of different sizes, it is obvious that the minimum observation
threshold must be adapted to each case in particular.
The minimum sample size in the case of Galicia is 162 observation per the year, there are 155
observations in the Basque Country and a minimum threshold of 100 annual observations has
been set for the Murcia Region. In all cases, there is also the requirement that there are
observations twelve months a year.
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Further, a second selection considers those classes that, even though they do not comply with the
aforementioned size criteria, have a high weight in the trade of the flow, origin and GU to one digit
to which they belong and they also have observations every month of the year.
2) The problem of the uniformity of the classes:
Given the definition of the elementary classes, all the products with the same units that belong to
the same GU to four digits and the same CUCI group are integrated in a single elementary class
and are processed as equivalent goods when calculating the unit value of the class. In the majority
of the cases, these products are, in fact, very similar, and the advantages associated to this
common treatment overcome the drawbacks of the aggregation. However, it will not be so in
some cases, which could lead to elementary classes that are too heterogeneous, so that the
estimated unit values will not be very representative of the prices of the operations effectively
carried out.
The uniformity of the classes cannot be directly measured according to the physical or technical
characteristics of the products that integrate the class, or for the dispersion of the prices that
integrate the operations; it is considered that there is a problem that must be processed when the
estimator of the unit value is unstable, with unstable estimator being taken to be one that has a
high variation coefficient. When obtaining the IVUs, it has been considered that the class is
sufficiently stable if the variation coefficient is under 35%.
This restriction would leave out of the selection those classes with a heterogeneous composition,
where the estimation of the unit value is not very robust, and which has a high trade volume. Thus,
instead of estimating the unit values as weighted averages of the prices of all the operations
performed, a robust estimate procedure based on L-estimators is used. r1+r2 trimmed means are
used, where each individual price is weighted by the relative amount (weight or number of units)
of each record with respect to the total effective observations. The r1+r2 trimmed means are
obtained by eliminating the [nr1] operations with the lowest prices and the [nr2] operations with the
highest prices from the total n observations of each class.
The procedure used to decide the trimming type is as follows: the variation coefficient is calculated
for each selected class. If this is lower or equal to 35%, the class becomes part of the selected
ones. And if the variation coefficient is over 35%, the following are calculated:
a) The variation coefficients of the following trimmed means, 0+0, 0+5, 5+0, 5+5, 0+10, 10+0,
5+10, 10+5, 0+15, 15+0, 10+10, 5+15, 15+5, 10+15, 15+10, 15+15, where the first digit
represents the trimming of the lowest prices and the second digit the highest.
b) The intraclass coverage of the same trimmed means, which is defined as the quotient between
the total value of the operations effectively used to estimate to unit value and the total value of the
initially available operations.
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
The trimming that satisfies that the variation coefficient is under 35% provided that the intraclass
coverage is over 50%.
The following table shows the number of selected elementary classes in the IVUs of the three
autonomous communities between 2000 and 2008. It can be seen how the growth in commercial
trade results in a larger number of operations and therefore in being able to have a greater
number of elementary classes that comply with the conditions set to be selected. In Galicia, the
number of selected classes rose from 416 to 744, which was an increase of 80%. The IVU of the
Basque Country are the one that select the largest number of elementary classes, in keeping with
the greater volume of its foreign trade, rising from 746 classes in 2000 to 1002 in 2008, 35% up. In
the Murcia Region, a total of 376 classes were selected in 2000, which were 50% higher in
number (559) in 2008.
Table 1. Number of elementary classes selected annually to calculate the IVUs
Elementary Classes
Year
Galicia
Basque
Country
Murcia
Region
2000
416
746
376
2001
426
742
403
2002
519
832
448
2003
591
894
460
2004
599
927
453
2005
649
954
491
2006
668
981
481
2007
719
1005
549
2008
744
1002
559
It seems obvious that the annual selection of classes may notably improve the quality of the
estimated IVUs in relation to other indexes that keep the same selection of classes of the base
year, particularly in periods where there is a significant increase of the economic phenomenon
studied.
Table 2 shows the distribution of the statistical value of the total foreign trade and of the
elementary classes selected for each flow by GU to one digit. It is evidently desirable that both
distributions are reasonably similar.
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Table 2. Distribution of the statistical value of foreign trade and of the elementary classes
selected by flow and usage group, average for 2000-2008
Foreign trade
Murcia
Region
Basque
Country
Galicia
Distribution by flow and usage
groups (%)
Selected classes
Exports
Imports
Exports
Imports
Consumer goods
54,1
26,1
49,8
37,5
Capital goods
13,3
6,0
5,1
9,6
Intermediary goods
32,6
68,0
45,0
52,9
Consumer goods
16,9
10,8
24,3
29,4
Capital goods
15,8
6,3
16,1
13,8
Intermediary goods
67,3
82,9
59,6
56,8
Consumer goods
68,8
14,5
73,9
13,9
Capital goods
4,7
5,5
3,4
5,1
Intermediary goods
26,5
80,0
22,6
81,0
The foreign trade of the three autonomous communities not only show differences in terms of the
volume of their operations and the evolution in the period considered, as indicated in the
introduction to this document, but the above tables also show a different distribution of these
operations by product groups according to their use. Special mention should be made of the
different structure of its exports. It is important to stress the lower relative economic weights of the
international flows of capital goods in the foreign trade of the three autonomous communities and
therefore if we also consider only the elementary classes that we have selected.
Table 3 shows the different indicators of the elementary classes selected in the IVU.
Table 3. Characteristics elementary classes selected by flow and usage group. Simple
average for 2000-2008.
Murcia
Region
Basque
Country
Galicia
Characteristics of the selected
elementary classes
Consumer goods
No annual observations
Exports
Imports
Intraclass coverage
Variation coefficient
Exports
Imports
Exports
Imports
4.510
1.212
97,9
97,9
11,5
15,4
Capital goods
898
219
94,8
94,7
17,8
23,0
Intermediary goods
686
591
97,2
95,7
17,4
19,4
Consumer goods
673
805
98,8
96,9
13,9
17,5
Capital goods
412
289
95,5
94,1
17,5
22,1
Intermediary goods
1.107
812
96,9
95,6
16,7
19,9
Consumer goods
1.505
940
98,5
97,3
3,1
4,8
Capital goods
108
117
95,6
93,4
20,2
20,6
Intermediary goods
266
250
96,5
95,8
10,3
9,7
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
The number of observations of the selected elementary classes is very different depending on the
type of good in question. There are less observations for capital goods which greatly hinders the
selection of classes of these goods when only considering the size criterion.
The intraclass coverage provides an idea of the trimming to which the selected elementary
classes have to be submitted to estimate their unit value, with the values are over 90% in all the
cases.
Finally, the variation coefficient is an indicator of the dispersion of the prices of the observations
that enter into calculating the unit values of each elementary class. The maximum values of the
variation coefficients are over 20% in the classes corresponding to capital goods flow.
In general, the elementary values corresponding to consumer goods trade have a very high
number of observations, high intraclass coverage and a lower variation coefficient. These are
therefore the IVUs that a priori produce greater confidence.
The imports of capital goods
represent the opposite case, with a lower number of annual observations and a high variation
coefficient. These are the IVUs that may present greater problems of stability and coverage, but
which correspond with flows of less economic importance.
2.5 Calculating the simple indexes of the elementary classes.
The simple indexes are the lowest level components used to obtain indexes and where there is no
weighting. They are elementary class indexes.
Elementary class indexes are calculated by applying the standard Paasche and Laspeyres
formulas, which enable the Fisher indexes to be obtained, which are the ones that are published.
These formulas can be consulted in the methodologies available by any of the statistics entities of
the three autonomous communities.
2.6 Designing the aggregation mechanism to construct composite indexes.
The Statistical Office of the European Communities (EUROSTAT) in SEC 95 (10.63) indicates
that: “The most appropriate way to measure the year-on-year price variations is by means of a
Fisher price index. The price variations for longer periods will be obtained by chaining the year-onyear price movements”.
Furthermore, the import and export price index manual prepared by the following entities:
International Labour Office (ILO), International Monetary Fund (IMF), Organization for Economic
Co-operation and Development (OECD), Statistical Office of the European Communities
(EUROSTAT), UN Economic Commission for Europe (UNECE) and the World Bank, recommends
the use of exact or superlative indexes as aggregation forms, specifically the Fisher, Walsh and
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
Törnqvist-Theil indexes. As far as the use of chained indexes are concerned, it recommends
chaining if the prices and quantities of the adjoining periods are more similar than the prices and
quantities of more distant periods.
Taking the above recommendations into account, together with the high volatility of the value and
of the traded products
The use of Fisher indexes implies that the index aggregation formula is the geometric mean of the
Paasche and Laspeyres indexes. Both types of indexes are therefore first calculated with the
relevant aggregation formulas of the simple indexes and their weightings.
The main advantage of the chained indexes is to keep an updated assessment structure, thus
avoiding the problems of ageing and the replacement biases that a fixed base is likely to generate.
On the other hand, this methodology has the drawback of the generalised loss of transversal
additivity and in a lower time average.
The drawbacks arising from non-updating of the base period emerge from the introduction or
elimination of products, technical changes or of preferences, etc, which lead to elementary classes
appearing or disappearing or which change their internal composition (composition effect) with the
resulting unit value change without it being the result of a change in the prices of the individual
products. It can also occur that the seasonal dynamics present in the base period, and which
influences the calculation of the unit value in this period, is modified over time which would also
deteriorate the comparability.
The way of solving the problem arising from these factors consists in performing comparisons
between periods that are as near as possible (for example, one period) by means of links.
The index below between two periods 0 and t will be the product of the links of each of the
intermediate periods (1,2,... t.1, t). This type of index lacks a base period in the strictest sense. It
has a period in which it is arbitrarily 100. This period is known as the "benchmark".
The application of the concept of the chained index to high frequency economic series (monthly or
quarterly) raises two significant problems:
1. The ranges introduced by the seasonal components (approximately periodic) and irregular,
which may distort and complicate, particularly the comparison between two adjacent period.
2. It is of interest that the high and low frequency estimates are quantitatively consistent, that is,
that the low frequency data may be derived from the high ones.
With respect to the first point, the base price and elementary classes may be seasonal and it was
therefore considered to deseasonalise them by means of using an annual benchmark. With
respect to the second point, the use of monthly (quarterly) chaining in monthly (quarterly) indexes,
that is, the linking of indexes by comparing current prices with those of the previous month
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
(quarter) may lead to systematic or derived deviations away from its annual equivalent. This
derivative is greater the more intense and stable the seasonal guideline is, or, if your prefer, the
more different the annual subseries of the monthly (quarterly) index are with respect to the annual
series obtained by their time aggregation.
Taking the above into account, it was decided to use chaining with respect to the previous year
(annual chaining). There are different annual chaining methods, by using the annual information
(annual overlapping) to select classes and calculate the base prices or by using a sub-period of
the previous year as can be the last month (monthly overlapping). The use of this second
possibility is based on the rupture that occurs when the first month of a year is compared with
respect to the last month of the previous year is less in this case.
The use of the annual overlapping has the advantage of having the same structure as its annual
equivalent, therefore the monthly links are temporarily consistent with the annual ones, fewer
discontinuities occur in the monthly overlapping but the time consistency is lost and additional
seasonal and irregular variation sources may be introduced.
These considerations mean that the selected classes and the base prices are considered to take
the structure of the immediately previous year as the benchmark and thus guarantee the time
consistency.
Therefore, the unit value indexes of Galicia, the Basque Country and the Murcia Region are
calculated as chained Fisher indexes with annual overlapping.
2.7 Calculating the aggregate IVUs by usage groups.
Each the elementary classes are selected that enter into the IVU calculation, the links of each
elementary class are calculated and are aggregated to calculate the links per usage group to four
digits, flow and origin.
Using these links, the grouping process is repeated to obtain the following aggregates until the
links for each flow are achieved. It should be considered that the information of all the classes,
whether selected or non-selected, is used in the weightings used in the aggregation method.
The chained indexes are then calculated by multiplying the links of all the intermediate period, so
that if we begin the calculation in year 0, the index in year 1 coincides with its link, the index in
year 2 is obtained by the product of the year 1 link and the relevant monthly link of year 2. For the
remaining years, the chained annual index of the previous year is multiplied by the monthly link
that always takes the previous year as the base.
Finally, the indexes are passed to the year 2005=100 benchmark.
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2.8 Processing the non-selected classes.
Unlike what occurs in other price indexes of the economy (industrial, consumer prices or prices
received by the farmers, for example), all the elementary classes that make up foreign trade are
involved in calculating the aggregate IVUs. This implies that it is necessary to assign an IVU to
those classes where there is not suitable information available in the customs records. In any
event, a fundamental requirement of the system is that every elementary class has its IVU, either
calculated using its own commercial operations or allocated based on other IVUs.
The allocation procedure is as follows, both for Laspeyres and for Paasche indexes: Once the
links are calculated according to the above section for the different aggregation levels of the usage
groups where the starting points was the links of the selected elementary classes (with
information), a descending allocation process in the aggregation level in the performed (from the
highest degree of aggregation to the lesser degree), for example, if any flow x zone cross does not
have information to calculate the link, the link of the relevant flow is allocated and so on
successively, by using the allocated links where necessary in each step until the elementary class
is reached.
This allocation system guarantees that if the process of obtaining aggregate links is replicated
using elementary classes with information and the allocated, the links remain unaltered.
2.9 Debugging.
One of the main drawbacks of the IVUs is their high volatility, as they reproduce the irregularity of
the customs statistics, which are their raw material, the frequent errors committed in the recording
when they fill in the fields of weights and units in their customs returns also result in extreme unit
values. Furthermore, the “composition effect” is another standard source of atypical values.
Therefore, these atypical values need to be debugged to be eliminated their effect on the final
indexes as far as possible. The debugging process that was performed was the following: given
that a uniformity criterion is required for the elementary classes by using all the annual
information, which sets as atypical values those records that make the variation coefficient of the
class is superior to 35% and subsequently, the selected type of trimming is used with the annual
information to carry out the monthly trimming, it may occur that an observation is atypical taking
into account the annual information but not from the monthly point of view. Therefore, those
records that are eliminated and which are not considered atypical when the monthly procedure
was performed were excluded when calculating the unit values, provided that the intraclass
coverage does not fall by 50%.
After this primary debugging, the procedure consisted in obtaining for each aggregate (beginning
by the greatest to the lowest degree of aggregation and restricting the process to the level of two
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
GU digits) a measure of the variability (typical deviation) of the links for the whole period and
analyse and study the months where these links are outside the interval (1+2, 1-2)), with 
being the typical deviation. The classes that are included when calculating the links that take
values outside the defined interval are analysed each month. It is determined which of them are
responsible for the data considered to be atypical and the extreme observations are eliminated
until said link takes a value considered to be acceptable.
3. Disseminating the IVUs
Once IVUs of each autonomous community to
the maximum level of desegregation are
calculated, it is decided which ones can be published. As a general rule, the indexes that are
published are the only ones that really are reliable in terms of their representation and coverage.
Obviously, the more they are desegregated, the greater the representation problems are of the
unit value indexes and the greater their volatility, as there is a high irregular component.
In the three autonomous communities, the IVUs are published by flow and by flow and usage
group to one digit: intermediary, capital and consumer goods, also considering the
origin/destination of the flows.
In the case of Galicia and the Basque Country, the indexes are published for the four geographical
zones used when defining the elementary classes: EMU, EU, OECD and the rest of the world.
The smaller size of the Murcia Region has meant that it was decided not to be publish the OECD
and the rest of the world indexes separately to avoid publishing indexes based on very few and
therefore not reliable series. Only two geographical zones are therefore considered: EU and the
rest of the world. Therefore, only the EU indexes are comparable by geographical
origin/destination, with the aforementioned clarification that the EU-27 in the Basque Country and
the Murcia Region and the EU-25 are considered in the Galician indexes.
The indexes by usage group to two digits are published, by considering the consumer goods (nonfood and food consumer goods) and intermediary goods (intermediary goods of agriculture,
livestock, forestry and fisheries, energy and industrial)
The low number of month records of capital goods flows means that their IVUs are excessively
volatile and not very relevant for the economic analysis, and they are therefore not published to
two digits. The usage group indexes to two digits are not desegregated geographically.
Table 4 provides the coverage of the IVUs of the three autonomous communities for the usage
groups to two digits, defined as the percentage of the total value of the operations of the
elementary classes selected out of the total value of the aggregate.
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Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
It has to be taken into account that the coverage is calculated excluding the goods of the CUCI
that have been initially eliminated and in the case of the Murcia Region, always considering the
imports of the CUCI 333 weighted by its corrector coefficient.
Table 4. Final coverage of the IVUs calculated by usage group. Simple average for 20002008.
IVU Coverage by flow and usage groups
Galicia
Consumer Goods
Capital Goods
Intermediary
Goods
Basque Country
Consumer Goods
Capital Goods
Intermediary
Goods
Murcia Region
Consumer Goods
Capital Goods
Intermediary
Goods
Exports
Imports
Total
95,5
94,8
Food
95,2
97,1
Non-Food
95,6
93,0
Total
89,5
54,5
Total
84,5
82,8
Agriculture
29,1
35,3
Energy
72,2
77,7
Industrial
85,7
86,4
Total
92,0
89,1
Food
89,2
93,0
Non-Food
82,5
87,1
Total
73,4
66,2
Total
91,6
88,5
Agriculture
14,9
46,9
Energy
81,8
93,1
Industrial
92,2
87,3
Total
91,6
78,8
Food
98,7
96,6
Non-Food
57,6
61,7
Total
75,3
76,1
Total
84,1
85,1
Agriculture
52,9
54,3
Energy
93,2
92,7
Industrial
84,5
77,1
15
Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.
The information provided by the previous table allows to confirm how the coverage of some IVUs
decrease as the level of desegregation increases, with the lower coverage being reached in
agricultural intermediate goods.
The IGE also publishes the IVU by branch of activity, without considering the geographical
origin/destination. Indexes of 23 branches of activity are published for imported products, 18
export branches of activity and sections of the NACE-09.
In the Basque Country, monthly data of the IVUs are published referring to the series at aggregate
level of the total exports and imports. The rest of series are disseminated grouped by quarter, in
the same way as all the foreign trade information published by EUSTAT. Nonetheless, the monthly
indexes with which the quarterly indexes are built have been considered in this joint publication of
the three autonomous communities.
Due to the fact that the foreign trade data of a year are modified each month that information is
received and are not final until ten months after the year end, the results will be provisional until
the foreign trade data are final.
16
Chained unit value indexes of Galicia, the Basque Country and the Murcia Region. Methodological document.