Guidance

UK House Price Index Quality Assurance of Administrative Data

Updated 14 December 2023

1. Executive summary

First launched in June 2016, the UK House Price Index (UK HPI) is a joint production by HM Land Registry, Land and Property Services Northern Ireland, the Office for National Statistics and Registers of Scotland. The UK HPI has been published initially as an experimental statistic. We have now implemented all the improvements and are seeking designation for the UK HPI as a national statistic.

The construction of the UK HPI is complex and brings together a number of comprehensive administrative data sources. The data used in the compilation of the UK HPI can be categorised as follows.

1. Price data from HM Land Registry for England and Wales, Registers of Scotland and HM Revenue & Customs (HMRC); Stamp Duty Land Tax sales for Northern Ireland processed by Land and Property Services Northern Ireland (LPSNI).

2. Data on the attributes of data sold from the Valuation Office Agency, LPSNI Valuation List and Energy Performance Certificates Scotland.

3. Demographic characteristics of the area in which the property is located through the Acorn dataset, produced and licensed by CACI.

Incorporating so many different data sources into any statistic, involves a certain degree of risk. Administrative data, in particular, may be collected and compiled by third parties, outside the Code of Practice for official statistics.

To further assure ourselves and users of the quality of our statistics, we have undertaken a thorough quality assessment of these data sources. This assessment is a continuous process, and we will publish updates periodically.

We have followed the Quality Assurance of Administrative Data (QAAD) toolkit, as described by the Office for Statistics Regulation (OSR). Using the toolkit, we established the level of assurance we are seeking (or “benchmark”) for each source. The assurance levels are set as either “basic”, “enhanced” or “comprehensive”, depending on:

• the risk of quality concerns for that source, based on various factors, such as the source’s weight in the headline index, the complexity of the data source, contractual and communication arrangements currently in place, and other important considerations
• the public interest profile of the item which is being measured, and its contribution to the headline index

Through engagement with our suppliers, we have assessed the assurance level that we have currently achieved by considering:

• the operational context of the data; why and how it is collected
• the communication and agreements in place between ourselves and the supplier the quality assurance procedures undertaken by the supplier
• the quality assurance procedures undertaken by us

Table 1 below summarises the quality assurance benchmarks that were set, and the assurance levels that we have assessed each source at during this assessment.

Table 1: Summary of administrative data sources used to produce the UK HPI and level of assurance applied to each source

Administrative data source	Data supplier	Assurance level
Administrative data used to produce UK HPI
Property sales transaction data	Property attribute data
Price Paid Data		HM Land Registry	Enhanced
	Register Data (Cash/Mortgage Indicator and Repossession volumes)	HM Land Registry	Enhanced
Scottish Land Register Data		Registers of Scotland	Enhanced
	Regulated Mortgage Survey	UK Finance	Enhanced
	Ordnance Survey Map Data	Ordnance Survey	Basic / Enhanced
	Council Tax Valuation List	Valuation Office Agency	Comprehensive
	Energy Performance Certificates Scotland	Scottish Government	Enhanced
	Acorn data	CACI	Enhanced
Administrative data used to produce both UK HPI and NI HPI
Stamp Duty Land Tax data		HM Revenue and Customs	Enhanced
	Northern Ireland Valuation List	Land and Property Services Northern Ireland	Enhanced

As a result of this assessment, we have put in place an action plan to improve our quality assurance in some areas.

Statisticians in LPSNI have since made a significant effort to engage with staff at HMRC, and have increased their understanding of HMRC’s own assurance of this data. In March 2018 we published our quality assurance of sales data from Stamp Duty Land Tax returns. The remaining areas we are still working on are:

• ONS is looking to standardise their communication and engagement with the Valuation Office Agency given the potential wider use of the Council Tax Valuation List data across the office
• land registration transactions involving the creation of a new register, such as new builds, are more complex and an increase in applications has created a backlog for HM Land Registry. As a result, processing takes longer. Read about what we’ve done to reduce our backlog, our service standards and our future plans

We will continue to engage with our data suppliers to better understand any quality concerns that may arise, and to raise their understanding of how their data are used in the construction of the UK HPI.

2. Introduction

Our assessment of data sources is carried out in accordance with the Office for Statistics Regulation’s Quality Assurance of Administrative Data (QAAD) toolkit. We are striving for a proportionate approach to assessing the required level of quality assurance for the many and varied data sources used in the compilation of the UK HPI. We seek to highlight and address the shortcomings that we have identified, and reassure users that the quality of the source data is monitored and fit for purpose.

In this paper, we set out the steps we have taken to quality assure our data, and our assessment of each source. In section 3, we outline our approach to assessing our data sources. In section 4, we discuss the assurance levels we are seeking for each data source, and the resulting assessment. Finally, in section 5, we detail our next steps towards achieving full assurance.

This publication is part of an ongoing process of dialogue with our suppliers, to increase our understanding of any quality concerns in the source data, and to raise awareness of how it is utilised. Through this document, we aim to provide information and assurance to users that the sources used to construct the UK HPI is sufficient for the purposes for which it is used. We will, therefore, review this document every 2 years. For more information on our UK HPI measure please see our guidance document About the UK HPI.

3. Approach to assessment

We have conducted our assessment of data sources used in the UK HPI using the Office for Statistics Regulation’s QAAD toolkit. We took the following steps for each data source:

• establish the risk of quality concerns with the data
• establish the level of public interest in the item that the data are being used to measure determine benchmark quality assurance levels, based on the risk and public interest
• contact the suppliers of administrative data to understand their own practices and approach to quality assurance; generally, this consists of the following steps:
  • send out questions to our data suppliers requesting information on their quality assurance procedures conduct follow up meetings/discussions with our data suppliers to request further information and clarification
  • maintain ongoing dialogues with data suppliers to develop a better understanding of any quality issues in the data, and raise awareness of how the source data are used
• review our own quality assurance and validation procedures and processes
• conduct an assessment of each data source using the four practice areas of the Quality Assurance of Administrative Data toolkit:
  • operational context and data collection communication with data suppliers
  • quality assurance procedures of the data supplier quality assurance procedures of producer
• determine an overall quality assurance level based on our assessment
• if this assurance level does not match the benchmark assurance level, then put steps in place to work towards meeting the required assurance level
• review the quality assurance on an ongoing basis; we will publish a QAAD update every 2 years

3.1 Setting the benchmarks

In accordance with the QAAD toolkit, we have sought assurance for each data source based on the risk of quality concerns associated with that data source, and the public interest in the particular item being measured by that data source.

We considered a high, medium or low risk of data quality concerns based on:

• the importance of the data source in explaining the price of a property (in other words, what would we do if we didn’t have this data.
• the complexity of the data source; for example, whether it is compiled from a number of different sources,
• the existing contractual and communication arrangements currently in place
• other considerations, such as any existing published information on data collection, methodology or quality assurance, or mitigation of high-risk factors with the data

We considered a high, medium or low public interest profile based on:

• the level of media or user interest in the UK HPI or its sub-components
• the economic or political importance of the UK HPI
• any additional scrutiny from commentators, based on particular concerns about the data

Together the risk of quality concerns and public interest profile are combined to set an overall assurance level that is required for a particular source. This assessment is based on the following matrix, as provided by UK Statistics Authority (Table 2).

Table 2: Quality assurance matrix

Level of risk of quality concerns	Public interest profile: Lower	Public interest profile: Medium	Public interest profile: Higher
Low	Statistics of lower quality concern and lower public interest [A1]	Statistics of low-quality concern and medium public interest [A1/A2]	Statistics of low-quality concern and higher public interest [A1/A2]
Medium	Statistics of medium-quality concern and lower public interest [A1/A2]	Statistics of medium-quality concern and medium public interest [A2]	Statistics of medium-quality concern and higher public interest [A2/A3]
High	Statistics of higher quality concern and lower public interest [A1/A2/A3]	Statistics of higher quality concern and medium public interest [A3]	Statistics of higher quality concern and higher public interest [A3]

Source: UK Statistics Authority

3.2 QAAD practice areas

We have aimed to assess the quality of each data source based on four broad practice areas. These relate to the quality assurance of official statistics and the administrative data used to produce them: our knowledge of the operational context in which the data are recorded, building good communication links with our data suppliers, an understanding of our suppliers’ quality processes and standards, and the quality processes and standards that we apply. This is in line with the Office for Statistics Regulations expectations for quality assurance of data sources. The full assessments for each data source can be found in Annex A. Table 3 provides a breakdown of these practice areas.

Table 3: 4 practice areas associated with data quality

Operational context and admin data collection	Communication with data partners	Quality Assurance principles, standards and checks by data suppliers	Producers’ Quality Assurance investigations and documentation
Environment and processes for compiling the administrative data	Collaborative relationships with data collectors, suppliers, IT specialists, policy and operational officials	Data assurance arrangements in data collection and supply	Quality assurance checks carried out by statistics producer
Factors which affect data quality and cause bias	Formal agreements detailing arrangements	quality information about the data from suppliers	quality indicators for input data and output statistics
Safeguards which minimise the risks	Regular engagement with collectors, suppliers, and users	role of operational inspection and internal/external audit in data assurance processes	Strengths and limitations of the data in relation to use
Role of performance measurements and targets; potential for distortive effects		Explanation for users about the data quality and impact on the statistics

Source: UK Statistics Authority

4. Assurance level assessment

In this section, we provide links which describe each of our data sources, and consider the assurance level that we are seeking (or “benchmark”) for these. Within these links, we also summarise our current assessment of the data and outline any further steps that may be required to reach the benchmark assurance level. We will also use this process to build engagement with our suppliers to better understand the data source, as well as raising awareness of how the data are used in the UK HPI.

The quality assurance of administrative data (QAAD) used in the production of UK HPI are:

• HM Land Registry data used in the production of UK HPI
• Registers of Scotland data used in the production of UK HPI
• Sales data from Stamp Duty Land Tax returns (HM Revenues & Customs) used in the production of UK HPI/Northern Ireland House Price Index
• Regulated Mortgage Survey data provided by UK Finance used in the production of UK HPI
• Valuations Office Agency Council Tax Valuations List used in the production of UK HPI
• Land and Property Services Northern Ireland Valuation List used in the production of UK HPI/Northern Ireland House Price Index
• Scottish Energy Performance Certificates used in the production of UK HPI
• Acorn (CACI) used in the production of UK HPI

5. Action plan

In the previous sections, we have considered quality assurance for all data sources in our house price index.

Of the data sources we investigated, there are some that need further work to reach the level of assurance we are seeking.

To address these shortcomings, we will carry out further steps to improve our quality assurance. All outstanding actions are summarised below (Table 4), with details on what actions we intend to take to rectify them.

Table 4: Action plan

Provider	Action
ONS	ONS is looking to standardise its communication and engagement with the Valuation Office Agency given the potential wider use of the Council Tax Valuation List data across the office.
HM Land Registry	HMLR continues the work to achieve our application service standards and reduce our processing backlog. Our primary focus will always be the delivery of core land registration services as that is central to our pivotal role in the property and financial markets. In 2018 we will continue to reduce the backlog by: - redesigning and reshaping how we are organised for operational delivery - enhancing and expanding our digital services to make the conveyancing process simpler, faster and cheaper See our Business Strategy 2017 to 2022 for further details. Implementation: Quality Assurance of Administrative Data documentation will be updated in July 2018 to reflect this.

This version of the house price index QAAD is intended to act as a progress update.

Statisticians in LPSNI have made a significant effort to engage with staff at HMRC, and have increased their understanding of HMRC’s own assurance of this data. In March 2018 we published our quality assurance of sales data from Stamp Duty Land Tax returns.

We intend to continue engaging with our data suppliers and, where appropriate, put in place firmer ongoing communications mechanisms and data delivery agreements. Importantly, this QAAD is not intended to serve as a final record of quality assurance. We view supplier engagement and feedback as an ongoing process, which we will continue to follow. We, therefore, intend to publish a review to this QAAD every 2 years.