CEGB cohort updates

This page contains information specifically for the participants in the "CEGB" cohort study. For further information please see the various studies and the privacy notice for participants is available on the site.

    Health Study change of lead researcher - 2024 update


    The health study on the group of CEGB workers employed in the late nineteen seventies and early eighties has changed lead researcher. Professor Tom Sorahan at the University of Birmingham, who had been involved in the study since 1995 retired in 2022. Dr Linda Nichols, now at the University of Warwick, and who had previously worked with Prof Sorahan, has taken over as lead researcher.

    These notes provide further information and follow on from the 2015 update about the study. All those in the study were employed by the CEGB for at least 6 months between 1952 and 1982. People in the study reading this will therefore almost all now be pensioners.

    Prof Sorahan database development

    The database was designed in the 1980s. The first task was to gather all the data from different CEGB regions, and the contract to collect it onto a single database was assigned to Prof Ray Cartwright, an epidemiologist at the University of Leeds. Prof Cartwright completed that work around the time of privatisation of the CEGB in 1990, and the Chief Medical Officers (CMOs) of each of the CEGB successor companies received a copy, stored on a magnetic tape soon after.

    Arrangements for data were very different then. Office computer systems were DOS based, rather than windows. Payroll data was computerised but there was still heavy reliance on paper records.  The confidential information on the magnetic tapes from Prof Cartwright was held securely by the CMOs.

    The questions posed by the study were straight forward – do the patterns of death in the electricity sector differ from those in the general population and, if this were to be the case, could the reasons be related to their work?
    Arrangements for managing the database fell to the Chief Medical Officers of the CEGB successor companies who collaborated to do this and created a steering group in 1991.

    They set up a contract with the Institute of Occupational Health at the University of Birmingham led by Prof Malcom Harrington CBE to undertake a study investigating the incidence of brain cancer in relation to electric and magnetic field exposure. The database was securely transferred to Prof Harrington. Soon after that he recruited a new epidemiologist to his team and thus (Dr as he was then) Tom Sorahan began work with data from the cohort of CEGB workers. In 1996 Linda Nichols, who was at the beginning of a career in research, joined the team.

    Prof Sorahan already had significant experience working with databases of worker groups in other industries. That gave him expertise on how to help organisations locate data missing from databases, and to identify duplicate entries.

    The Brain Cancer study, which used the data on the database and information provided on cause of death, was published in 1997.

    However, during the course of the study, it became clear that the data set had some duplicate entries and other inconsistencies, for example if the recorded job did not fit with the recorded location of work.

    CEGB successor companies, via their personnel functions, were asked to help clarify information. However, the information was not always easy to find. Prof Sorahan’s experience from work with other occupational databases helped him to understand where and how the companies’ staff should look. In turn, a process of cleaning the data was commenced, and clarification was sought from personnel records held by CEGB successor companies. It is almost certain that without both the expertise and persistence which Prof Sorahan bought to this, that the dataset would be much less complete.

    Over a period of several years the data cleansing process led to the identification of many duplicate records and the database of around 84,000 CEGB employees received at privatisation turned out to be one of 82,000 once the duplicate records were removed.

    With the improved data, an update to the Brain Cancer study of 1997 was published in 2001.

    Database registration and pseudonymisation

    Developing practice and legislation around the security of digitally stored personal data, administrative changes to how information on cause of death is provided, and extending the study so that cancer registration data can be linked, has required liaison between Prof Sorahan and the relevant authorities. Although this work is unseen, Prof Sorahan has undertaken a huge amount of work to ensure that relevant registration has been maintained. Some years ago now, pseudonymisation took place to comply with data security legislation, so that names are no longer stored, thus aligning the data set with the NHS system enabling linkage for example with cancer registration data via a unique identifier for each data subject.

    Published studies

    During the 27 years with which Prof Sorahan has worked with the database, he has been the author of a dozen published studies, most of which he led. Five of these papers were co-authored with Dr Nichols.

    Overall analysis of the database shows higher than normal rates of asbestos related disease. It was already well known that working practices which ceased many years ago meant that power station workers had been exposed to asbestos. This is therefore an expected result.

    The other expected result is that mortality rates are lower than for the general population. This is found in other worker cohorts, and is known as the healthy worker effect.

    Topics specifically investigated have mostly looked for a possible relationship between occupational exposure to electric and magnetic fields (EMF) and diseases including brain cancer, leukaemia, heart disease, neurodegenerative disease (Motor Neurone Disease, Parkinsons, Alzheimer’s). These studies have been negative. They do not show an association between Occupational exposure to EMF and any of the diseases investigated.

    Lead researcher change with change of data base registration

    Establishing this large Occupational database involved considerable foresight in the 1980s. From an epidemiological point of view, it’s an important resource for study.

    Prof Sorahan’s retirement means that the study, and its registered data set must be passed to a new lead researcher.
    Dr Linda Nichols, who first worked with Prof Sorahan on the database in the late 1990s, before moving to the University of Warwick seven years ago has accepted the role leading the study. She is arranging the transfer of the database to the University of Warwick. Legislative safeguards around the database, and data sharing agreements with NHS digital, mean that this process takes several months. As soon as it is complete she will be able to provide data subject access information, following the change from Prof Sorahan.

    Prof Sorahan’s work

    The nature of an epidemiologist’s work checking analysing and interpreting data, is by its nature largely unseen.  The reliability of the findings of a study depend on several factors including study design and the quality of the data. Prof Sorahan’s diligence, particularly in earlier work improving the accuracy of the data, has enabled a greater confidence in the reliability of the results of existing studies and of studies which may be carried out in future. Prof Sorahan’s work has added significantly to knowledge of the health of UK electricity generation and transmission workers, which has had particular importance in contributing to the world knowledge base on concerns about EMF and health.

    Further information 

    If you have any queries regarding this study, further information can be found in the privacy notice.

    If you think you might be included in this cohort, but do not want your data to be used for research, please contact the NHS England opt-out service at National data opt-out - NHS Digital

    Health Study reaches 30 year anniversary

    It is 30 years since the National Health and Safety Committee of the then CEGB agreed that a large group of employees (a “cohort”) should be enrolled in a study looking at causes of death in workers from the industry. The questions posed by the study were straight forward – do the patterns of death in the electricity sector differ from those in the general population and, if this were to be the case, could the reasons be related to their work? The study has been carried out by researchers at the Institute of Occupational and Environmental Medicine at Birmingham University, currently led by Professor Tom Sorahan.

    The study has shown that those who worked at power stations in the days when exposure to asbestos occurred have an increased risk, many years later, of developing mesothelioma – a particular form of cancer associated with asbestos. Otherwise, it has shown that electricity industry employees tend to live longer than those in the general population. This is a common finding in studies of working groups and it has been called the “Healthy Worker Effect” to reflect the fact that those in work are generally in better health than those who have not worked.

    The study has been extended in recent years so that it includes not just causes of death but also information on cancer registrations from the NHS cancer registry. Using this combination of data, the researchers have looked to see if there are any diseases associated with exposure to magnetic fields (produced by the flow of electricity and commonly called EMF). The main conditions of interest have been brain cancer, leukaemia, degenerative neurological diseases and certain heart problems.

    The findings, which have been published in medical journals over the years, have all been very reassuring with no suggestion that EMF cause any diseases. This is in line with the results of similar workplace studies conducted in other countries.

    All those in the study were employed by the CEGB for at least 6 months between 1952 and 1982 and, therefore, most are now pensioners. When the study began, it was accepted practice to obtain “bulk” approval from Company management and employee representatives rather than to seek individual consent but the latter would be the requirement nowadays if setting up a similar study. To take account of this change in research ethics, researchers handling the data no longer have access to the names of those in the cohort. Each person’s identity has been replaced by a number which was provided by the national body that oversees such research – the Health and Social Care Information Centre.

    The study was well known in the industry in the late 80s but many cohort members may have forgotten about it until reading this article. Professor Sorahan will ensure that any future publications appear in an open access medical journal so that if individuals wish to read them, they can obtain a free copy via the internet.