This dataset does not contain any directly identifiable personal information.

Postcode level information is extracted from the Assessors' Portal. Postcodes are used to assign data to data zones. The data is cleaned to ensure that all records are located in a data zone within the council area assigned by the Assessor. Records using out of date postcodes are also investigated to check that they are still placed in the correct data zone. Differences in total number of dwellings in a data zone outwith a threshold are investigated to determine if there is a reasonable explanation for the increase or reduction. Frequencies for variables (e.g. type of dwelling) are compared with earlier years' data to identify any potential issues. The results of postcode cleaning and quality assurance work are fed back to the Assessors' Portal each year.

Data on type of dwelling is obtained from the Assessors’ Portal. It is possible that not all information held on the Assessors’ Portal is up-to-date. Assessors are only able to reflect physical changes and alterations to dwellings once they have been sold and a reconsideration of the banding has taken place. Furthermore, it may take time for changes as a result of new building or demolition to be recorded.

When using data zone level information on dwellings and households, changes over time can occur not only as a result of new building activity and demolition but also because of changes related to the postcodes of dwellings. Postcode changes can occur due to improvements made to administrative systems or NRS data cleaning, re-locating postcodes which were previously allocated to an incorrect data zones. Differences can also occur due to postcodes being allocated to a different data zone because the distribution of their population has changed. These differences are likely to be minimal and have only a small effect on change over time except when looking at small numbers of data zones.

Attachment type of dwellings for 2015, and attachment type for some dwellings in Tayside for 2016, have been estimated by NRS and have not based directly on numbers extracted from the Assessor's portal in January. Information on attachment type was missing for 37,858 dwellings in Tayside in the January 2017 extract from the Assessors' Portal. Data was re-extracted in May 2017. Information about the attachment type of these dwellings in January 2017 was estimated by NRS based on their attachment type in May 2017. Of the 37,858 dwellings with missing attachment type in January 2017, 1 was found to be detached, 35,077 terraced and 2752 had unknown attachment type in May 2017. A further 28 dwellings were present in the January 2017 extract but not present in the May 2017 extract, possibly because they were demolished in the time between the two extracts being taken. These dwellings have been classed as having unknown attachment type in January 2017. Data on attachment type was not available for any dwellings in the extract taken in January 2016. The estimates for type of dwelling for 2015 have been estimated by NRS based on data extracted from the Assessor's Portal in previous and later years. Dwellings which were present in the January 2016 extract have been matched to their type and number of rooms information available from October 2016, January 2015 or January 2017, in that order. Therefore the attachment type information estimated for each dwelling may not be the same as that held on the Assessor's Portal as of January 2016, if for example the property was altered between January 2015 and January 2017.

The statistics are designed to be consistent, and incorporate comparable historical data where appropriate.

It is the policy of NRS to make its website and products accessible according to published guidelines. More information is available in the Accessibility section of the NRS website.

The statistics are mainly used for informing councils’ decisions about housing need and service provision.

Data for each year is downloaded from the Assessors’ Portal in late December of that year or early January of the following year, e.g. 2013 data was downloaded on 7 January 2014. It is published in the following summer.

In February 2019, we updated our methodology for allocating datazones to higher geographies to align with Government Statistical Service Geography Policy. This resulted in revisions to some aggregated figures at Electoral Ward and Scottish Parliament Constituency level.

A small revision was made to the figures for two data zones in Falkirk council area in 2012, for the years 2005 to 2009. This is to move around 20 dwellings to the correct data zone. The figures for the council area and for Scotland as a whole are unaffected by this change.

Revisions and corrections to previously published estimates are dealt with in accordance with the Scottish Government Statistician Group corporate policy statement on revisions and corrections - a copy of which is available on the Scottish Government website.