When a researcher obtains CPI from a health and adult social care provider in England with section 251 support, they should expect that, once that organisation has stated its compliance with the national data opt-out policy then the records of patients who have registered a national data opt-out will have been removed. This may mean that the dataset provided might not be complete.
When researchers receive data, where national data opt-outs have been applied, there is a potential to introduce bias to their studies which researchers will need to consider. For example, there might be higher levels of opt-out across certain geographical areas, age groups or specific conditions that might impact on the results of studies.
6.1.1 Available products for managing bias
There are several products and resources available to support researchers to manage and understand whether any bias may have been introduced into the data provided to them.
National data opt-out statistics – publication
NHS Digital produces a statistical publication on the volumes of national data opt-outs. It includes the number of people who have a national data opt-out, broken down by age, gender and a variety of geographical breakdowns.
National data opt-out - Hospital Episode Statistics analysis
NHS Digital has produced analysis showing the impact of removing opt-outs on Hospital Episode Statistics (HES), which can be downloaded from the page How the national data opt-out affects data released by NHS Digital. This provides counts on hospital episodes before and after national data opt-outs are applied to the following datasets:
- Admitted Patient Care (APC)
- Accident & Emergency
Further comparative analysis provides counts by gender, age bands, broad ethnicity, and clinical commissioning groups. In addition, for the APC data, analysis will be provided on primary procedure and diagnosis groups.
Information from the data provider
There is no requirement on the data provider to supply any information on the numbers of records removed from their disclosures of data; however, this is also not prohibited, provided this is done in a way that maintains confidentiality.
Numbers of records removed
When NHS Digital discloses data through its Data Access Request Service (DARS) the data recipient is provided with additional information to help them understand the impact of the application of national data opt-outs on the data provided. This includes the number of records removed and the number of unique patient records removed (as data releases can contain more than one set of data records for the same patient).
Other organisations may similarly provide details of the number of records and/or unique patient records removed but are not obliged to.
Bespoke analysis provided by data providers
Health and adult social care providers may wish to undertake more bespoke or specific analysis to help researchers understand the potential impact of national data opt-outs on the data that they receive.