(from January 2003)
During 2002 the methodological revision of the Hotel Price Index (HPI) started last year was continued. There was a consequent update in the form of a calculation and in the index database.
The modifications that have been introduced for 2003 are motivated by an adaptation to the calculation of other indices elaborated by the INE, by the demand for user information and, in their majority, by the improvement in the quality and interpretation of the results.
The following methodological modifications have been introduced into the index:
1. Weightings are calculated 1 different for each month.
2. The formula used is a linked Laspeyres index.
These modifications have implications both on the formulation of the index and its interpretation.
The simple indices 2 , on an establishment, tariff and province category level. The relation between the average price in a specific month of the current year and the average price in the same month the previous year are obtained now. s ( T

1 )
I sT jkt

M
M sT jkt s ( T

1 ) jkt

100

 precio medio en la precio medio en la tarifa tarifa t t categoría k provincia j en categoría k provincia j en el el periodo periodo objeto ( mes anterior ( mes s s , año
, año T
T )

1 )

100
In turn, the tariff prices t of periods (s,T) and (s,T-1) for the stratum jk , M sT and jkt
M s ( T

1 ) jkt
, are calculated as a simple geometric average of establishment prices.
Rooms occupied ( B ) in each tariff each month from the previous year that are used to obtain the weightings are calculated in the following way 3 : s ( T

1 ) jkt
 i e jk 

1 s
B ijk
( T

1 ) 
A s ( T

1 ) ijkt
 f s ( T

1 ) jk
1
The weightings of the less significant strata have been grouped into other strata.
2
The prices estimated for the less significant strata on a weightings level, have been grouped into other strata.
3 and represents the set of establishments in the sample who have responded to the questionnaire.
1

B s ( T

1 ) ijk
, number of rooms occupied in the hotel I of category k province j , (datum extracted from the questionnaire in each month of the previous year).
A s ( T

1 ) ijkt
, percentage of occupied rooms in the hotel I of category k in province j to which tariff t , is applied (data extracted directly from the price module questionnaire from each month of the previous year ). f s ( T

1 ) jk
, is the elevation factor in stratum jk .
1. Calculation of weightings
: total number of rooms occupied in the establishments of one category k and one province j to which the tariff t is applied in month s of year T-1. s ( T

1 )
L jkt

M s ( T

1 ) jkt

 j k t
M s ( T

1 ) jkt s ( T

1 ) jkt
 s ( T

1 ) jkt where B s ( T jkt

1 )
represents the total number of rooms occupied at tariff t , province j and category k in month s from the previous year, y M s ( T jkt

1 )
is the average price in tariff t , province j and category k in month s of the previous year. They are therefore, different for each month in such a way that each stratum (province/category/tariff) has a different relative importance according to the month we are in. These weightings L indicate the percentage of income received by hoteliers for double rooms with bathroom to which tariff t has been applied in category k , over the total of income as all tariffs in the total of establishments from this community in the specific month s .
The price M s ( T

1 ) jkt
for each month is that which is also used as a simple index reference in such a way that the monthly simple indices for the previous year for which the HPI is being calculated has been made equal to 100.
The Weightings s ( T

1 )
L jkt
are grouped ( W ) by tariffs, categories or according to geographical scope that is required (provinces or Autonomous Communities) to obtain weightings for all possible indices.
2. Calculation of linked index
From January 2003 the group formula used to calculate the HPI is a Laspeyres index linked annually. The reference period of the prices the same month the previous year for which twelve series of linked indices - one for each month - are obtained.
This formula guarantees the continuous update of the structure used in the weighting of the indices as the weightings are calculated always referred to the year immediately before. To ensure comparability of the indices obtained with different structures the linked index is used
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which avoids the need to calculate link coefficients for each index that is carried out. This is because the linked index is equivalent to the index calculated with the new structure linked forwards for which it is totally comparable with the previous indices calculated with different structures.
Another advantage of the linked index is that those indices that reach high levels during the year will not weigh more relatively in the group as in linking the indices calculated in the previous period, they are equal to 100 again.
The disadvantages on the other hand, of this new formulation are: the lack of additivity (it is not possible to obtain the index of any group as a weighted average of group indices that comprise it) and that the comparison of the index among different months (February with
January, for example) is not correct as different weighting structures have been applied each month. This means that the HPI interannual variation rate to analyse the evolution of hotel prices will be used exclusively.
The calculation of the index, over different periods, in the following way (for example by national tariffs):
Year: 2002
01
IPH s ( 02 ) t
   j
 k
01
I s ( 02 ) jkt

01
W jkt



01
W jt
Year: 2003
01
IPH s ( 03 ) t
 s ( 02 )
IPH t s ( 03 )  01
IPH t s ( 02 )
100



  j

 k s ( 02 )
I s ( 03 ) jkt
 s ( 02 )
W jkt



 s ( 02 )
W jt


 01
IPH t s ( 02 )
100
Year: 2004
01
IPH s ( 04 ) t

03
IPH t s ( 04 )  01
IPH t s ( 03 )
100 and this way successively. In a generic way,

03
IPH t s ( 04 )  02
IPH t s ( 03 )
100
 01
IPH t s ( 02 )
100
Year T:
01
IPH sT t

100
 b
T 

2002 b

1
IPH t sb
100 b up to T being all intermediate situations of the index in month s , starting with b in 2002.
In such a way that in the new formula, the HPI compares the current period ( s, T ) with the base period (2001) considering the intermediate situations b that are the HPI data in the same months s from previous years.
In using the structure for the previous period prices from the current period are being compared with prices from the same month the previous year. As to weightings, calculated as price per quantity, both factors are modified as prices and rooms occupied will be taken from the same month the previous year for which each month the HPI is calculated with the most current structure available, and in linking it, the data is made comparable with those from previous years.
Therefore, the reference period of the index (the level of the index value) is 2001 while the reference period of prices and weightings is the same as the previous month.
3

Therefore, twelve series of linked indices (one for January, another for February, etc.) that will have 2001 as a reference are obtained.
4