• Data reference period (Quarter)
• Geographic localization (NUTS - 2013)
• Category of housing unit
• Tax residence of the purchaser
• Institutional sector of the purchaser

• INSTITUTIONAL SECTOR:  Institutional units with a similar type of economic behaviour are grouped into institutional sectors. Institutional units are classified in sectors on the basis of the type of producer they are and depending on their primary activity and function, which are considered indicative of the units' economic behaviour. A sector is divided into sub-sectors according to its own criteria, which makes for a more accurate description of the units' economic behaviour. Each institutional unit belongs to a single sector or sub-sector.
• REFERENCE PERIOD:  The length of time for which data are collected, e.g. a specific day, month or year.
• HOUSEHOLD DWELLING:  Dwelling that is normally intended to accommodate only one family, on the condition that it is not being used for other purposes at the period of reference.
• TRANSAÇÃO:  Operação pela qual se transfere a posse de um bem mediante uma contrapartida.
• TAX RESIDENCE:  Place of habitual residence for natural persons, place of the head office or effective management for legal persons or, failing that, the place of their permanent establishment in Portugal.

`NTRANSj = sum_(i=1)^(n) NTRANSij`

                      NTRANSij, Number of transactions of dwelling i in quarter j