This study reports on the breadth and balance of public health research funded by the UK NIHR over a 7 year period. Over one-third of its research portfolio could be classified as being related to public health, according to the inclusion and exclusion criteria used in this study. This reflects recognition of the importance of this type of research. Interestingly, this represents a greater proportion than that identified in a review of research funded by the National Institutes of Health in the United Stated of America in a 2 year period from 2010 to 2012. That portfolio analysis estimated that almost one-fifth of its total research expenditure was allocated to disease prevention, although this difference may reflect the classification systems used [20].

All of the NIHR research programmes and schools had funded at least one project classified as being relevant to public health, which reflects that public health research is funded across the breadth of the NIHR. Unsurprisingly, all of the research funded by the PHR Programme and the SPHR related to public health, as their remit specifies this type of research.

There was a continual growth of active public health research projects over time. This may be explained partly by the development of new programmes. For example, the NIHR’s core research is located within the NHS, with specific funding for public health research increasing during the study period. However, it also recognises the impact on the NHS, and on the health of the nation, of a broader range of interventions and settings. Given this broader view a gap was identified in the funding of high quality, nationally important, evaluations of public health interventions in non-NHS settings [21]. This lead to the start of the PHR Programme in 2008 and SPHR in 2012.

Research was funded across all four of the domains of the Public Health Outcomes Framework. The largest category was ‘healthcare public health and preventing premature mortality’, which included just over one-half of the public health research projects. Projects within ‘healthcare public health’ included those considering the accessibility and redesign of health services provided by the NHS. ‘Preventing premature mortality’ projects include those that aim to prevent mortality from conditions such as cardiovascular disease and diabetes. The large number of projects within the ‘healthcare public health and preventing premature mortality’ category reflects that the NIHR funds research on behalf of the NHS, social care and public health and puts patients and the public at the centre of everything they do. There were a very low number of projects funded within the category of ‘improving the wider determinants of health’. Projects funded within this area included those considering housing, transport and employment. In their 2010 study, Bambra et al. considered that modifying lifestyle interventions are often easier to identify and research than those concerning wider social determinants of health and health inequalities [22]. However, these types of projects may be covered by the PHR Programme and the SPHR, which are still in their early stages of funding studies. Furthermore, the DH Policy Research Programme (PRP), which supports research on the development and evaluation of ‘policy’, as distinct from ‘practice’, funds research on wider determinants of health, some of which is done in collaboration with other government departments.

The most prevalent illness/condition for the research projects was ‘mental health and behavioural conditions’, which accounted for approximately one-quarter of projects. As well as covering mood disorders, such as depression, this category also included self-harm, domestic violence and health behaviours, such as alcohol use, smoking and substance use. Mental health is a significant health concern in the UK, which has recently prompted a number of government strategies, such as ‘No health without mental health’ [23]. This emphasised the important link between good mental health, physical health, and wider social and economic benefits.

The second most prevalent illness or condition researched was ‘infectious diseases’ which accounted for 13 % of public health projects. These projects were primarily within the ‘health protection’ domain and, for example, included projects focused on vaccination programmes. The importance of this type of research has been highlighted to provide safe, cost effective and efficient means of preventing illness from infectious diseases. The high proportion of research projects echoes the value of this type of research, which was highly prevalent in the Wellcome Trust’s portfolio review [3]. Other ‘health protection’ studies are funded by NIHR or the PRP. However, the 13 NIHR Health Protection Research Units were not established until April 2013 and are therefore outside this study.

An important outcome of the study has been linking examples of NIHR funded public health research to public health guidelines issued by the National Institute for Health and Care Excellence (NICE). These are UK ‘guidelines on public health topics [that] make recommendations on local interventions that can help prevent disease or improve health’. Since February 2014 the guidelines have included a section for ‘Relevant ongoing NIHR research’. This gives public health professionals and academics examples of research studies related to the guideline topic that are in progress or at a pre-publication stage.

This study is limited because it is a descriptive analysis of the breadth and scope of public health research funded. To get an indication of the actual value of the research to practice would require future assessment of the impact of the research findings. This would be a useful exercise to reflect whether the NIHR is funding projects with direct relevance to improving population health. Measures of impact can include citation in scientific publications, citation in public health guidance and inclusion in information relevant to policy. However, for many research projects in this portfolio analysis it is considered too early to assess their impact at this time. This is an important consideration for the future. Approaches to assess impact could include analysis of case studies and qualitative interviews of study investigators and evidence users.

The main limitation of this study was defining what exactly constitutes a ‘public health research project’ and therefore which projects should be included in the study. Obtaining views from specialists within the public health field revealed many different opinions of what should be included, relating to the wide range of practice and interests within public health. The inclusion criteria were purposively wide, to capture projects within all four of the domains of the Public Health Outcomes Framework. A similar difficulty in classifying public health research projects was experienced by researchers who compiled an inventory of Swedish public health research in 2005 [8]. The authors of a report of public health research funded in Europe also emphasised the difficulties in agreeing on a concept of public health [24]. An overview of the literature for European research in health management over a 10 year period from 1995 to 2005 concluded that, ‘Public health is not a well-defined discipline with clear boundaries in research terms since it includes contributions from a wide range of social and behavioural sciences’ [25]. Consequently, this has made the task of searching the databases both especially complicated and perhaps a more subjective exercise than might have been desirable.

Another major limitation for this study’s methodology is that a universally recognised taxonomy for public health research projects does not exist. Therefore, using alternative taxonomies may present a different picture of the research. The NICE taxonomy was used for this study and enabled linking examples of NIHR funded public health research projects to NICE public health guidelines. The Public Health Outcomes Framework was also used because this was developed by the Department of Health in 2012 as a way of measuring outcomes for the public health system [13], and so it applies to UK public health practice. These coding systems were deemed relevant and acceptable for use in the current study. However, the classification schemes used, and other possibilities identified, all have limitations that can affect generalisability to other settings. The lack of a universally accepted classification scheme for public health research is a barrier to the reproducibility and comparability of results. Therefore the authors suggest that developing a public health-specific taxonomy is a priority for the public health community. The need for the development of a better classification scheme is an identified knowledge gap from this work. In this context, it is interesting to note that a classification of public health interventions is being developed for the World Health Organization International Classification of Health Interventions. The classification aims to provide ‘a common tool for reporting and analysing the distribution and evolution of health interventions for statistical purposes’ [26]. The inclusion of public health interventions is a development of interest in this field.

Mapping a research funder’s public health portfolio enables identification of the number and type of research projects within specific areas, such as by illnesses and conditions. This can pave the way for the identification of priority areas for the commissioning of future research. Appropriate research priority-setting is an integral part of a needs-led research agenda. Future evaluation is recommended to ensure the value of research, for example continuing to evaluate the portfolio by further in-depth analysis in particular areas, such as health inequalities or specific population groups.