- Original Article
- Open Access
Radiological research activity 1998–2007: relationship to gross domestic product, health expenditure and public expenditure on education
© European Society of Radiology 2010
- Received: 23 May 2010
- Accepted: 7 July 2010
- Published: 28 July 2010
The purpose of this study was to evaluate the relationship of the radiological research activity from 1998 to 2007 to the gross domestic product (GDP), health expenditure and public expenditure on education.
The population-adjusted research activity determined by the number of articles published, the cumulative impact factor (IF) and the cumulative IF per capita were correlated with per capita values of the GDP, health expenditure and public education expenditure. Linear regression analysis and multiple regression analysis were used for statistical analysis.
The cumulative IF per capita correlated with the GDP per capita (R = 0.94, P < 0.0001), health expenditure per capita (R = 0.93, P < 0.0001) and public expenditure on education per capita (R = 0.93, P < 0.0001). Multiple regression analysis demonstrated that public expenditure on education was an independent predictor of radiological research activity (P < 0.001), whereas the year, GDP and health expenditure did not reach statistical significance (P > 0.05).
Radiological research activity demonstrates a close relationship to the GDP, health expenditure and public expenditure on education. The last factor independently predicts research activity.
- Impact factor
- Research activity
- Gross domestic product (GDP)
- Health expenditure
- Public education expenditure
Research requires financial resources [1, 2]. This may apply particularly to heavily technical fields such as radiology with large amounts of capital expenditure . Increasingly, funding depends on evidence of favourable terms , and that resources for research are adequately employed. The situation is complicated by the fact that scientific research activity not only depends on project-related finances but also on the available research and medical infrastructure, such as dedicated research coordinators , faculty size , clinical workload , history of mentoring and pressure on productivity. Studies regarding the relationship between funding  or different macroeconomic variables and research activity have been published for various other medical disciplines and health topics in the past [7–19]. In radiology, research activity has been benchmarked according to population size [20, 21], GDP  and geographic region [20, 21, 24].
To the best of our knowledge, no study has analysed worldwide radiological research activity in relation to a set of socioeconomic parameters including population size, GDP, health expenditure and public expenditure on education. Thus, the purpose of our study was to evaluate the relationship of the radiological research activity over one decade to the GDP, health expenditure and public expenditure on education.
Radiological research activity was determined between 1998 and 2007 on the basis of bibliometric data obtained from the most commonly cited radiology, nuclear medicine and medical imaging journals . To estimate the quantity of research activity, the total number of publications was determined. To reflect research quality, the mean impact factor (IF) was determined, and to estimate quantity and quality, a cumulative IF was calculated (by summing the IFs of all publications for a given year). The IF of the individual journals was taken from the Thomson ISI Web of Knowledge/Science database (http://apps.isiknowledge.com). The research activity was correlated with the socioeconomic factors population, GDP, health expenditure and public expenditure on education by calculating the following indexes: cumulative IF/population (in millions), cumulative IF/GDP (in current billions US$), cumulative IF/health expenditure (in current billions US$) and cumulative IF/public education expenditure (in current billions US$).
To obtain reliable socioeconomic parameters, we searched data that were as complete as possible for the selected countries between 1998 and 2007. To obtain comparable results, the data had to be from one single database. According to these specifications, we obtained the total population, GDP at market prices (in current billions US$), health expenditure per capita (in current billions US$) and public education expenditure as a percentage of GDP from the online databases of the World Bank  in October 2008.
Data on health expenditures were available in these databases for the period between 2001 and 2005. Data on public education expenditures were available from 1998 to 2005 but not for all countries throughout the entire period between 1998 and 2005.
Mean impact factors (IF) for the analysed journals, 1998–2007
American Journal of Neuroradiology
American Journal of Roentgenology
Applied Radiation and Isotopes
British Journal of Radiology
Cardiovascular and Interventional Radiology
Clinical Nuclear Medicine
European Journal of Nuclear Medicine and Molecular Imaging
European Journal of Radiology
Human Brain Mapping
IEEE Transactions on Medical Imaging
International Journal of Radiation Biology
International Journal of Radiation Oncology Biology Physics
Journal of Clinical Ultrasound
Journal of Computer Assisted Tomography
Journal of Magnetic Resonance Imaging
Journal of Nuclear Medicine
Journal of Ultrasound in Medicine
Journal of Vascular and Interventional Radiology
Magnetic Resonance Imaging
Magnetic Resonance in Medicine
NMR in Biomedicine
Nuclear Medicine and Biology
Nuclear Medicine Communications
Physics in Medicine and Biology
Radiation Protection Dosimetry
Radiologic Clinics of North America
Radiotherapy and Oncology
RöFo-Fortschritte auf dem Gebiet der Röntgenstrahlen
Ultrasound in Medicine and Biology
Ultrasound in Obstetrics and Gynecology
For article selection, a search was performed on the ISI database in August 2008. All original articles that appeared in the selected journals between 1998 and 2007 and were cited on the ISI database were included. Other types of publication such as reviews, letters, book reviews, editorial materials, meeting abstracts, meeting summaries, news items, notes or proceedings papers were not included.
To restrict the total number of countries to a reasonable number, countries were included in our analysis when at least 90 articles were published within at least 1 year during the 10-year study interval in the selected journals. The following 24 countries fulfilled the inclusion criteria: Australia, Austria, Belgium, Brazil, Canada, China, Denmark, Finland, France, Germany, Greece, India, Israel, Italy, Japan, the Netherlands, Poland, South Korea, Spain, Sweden, Switzerland, Turkey, the UK (England, Wales, Scotland and Northern Ireland), and the USA.
Number of articles
For each country the total number of articles per year and per journal was determined using the ISI web program. One count was given to every country listed as part of the address information/author affiliation. Multiple country counts were assigned to articles with authors from multiple countries.
For each country the articles published within 1 year were determined and assigned to their respective journals using the ISI web program. A product was calculated by multiplying the number of articles published in a journal with the journal’s corresponding IF for that particular year. Then, the products of all selected journals were added to get the cumulative IF for each country per year.
Mean cumulative IF
A mean cumulative IF was calculated by dividing the sum of several cumulative IFs of each country throughout the time period (in years) that was studied. The time periods for the socioeconomic factors varied based on the availability of the data in the World Bank.
For each country the mean impact factor was calculated by dividing the total cumulative impact factor over the entire study time by the total number of articles published.
Ratios were calculated for cumulative IF/GDP, cumulative IF/health expenditure and cumulative IF/public education expenditure. The trends of these ratios over time are demonstrated with line charts. Linear regression analysis was used to assess the effects of per capita values of GDP, health expenditure and public education expenditure on cumulative IF per capita. All variables were analysed on logarithmic scales. Multiple regression analysis was used to find independent predictors. We used SPSS software (version 16.0.1, SPSS, Chicago, IL, USA) to perform the statistical analysis. Two-sidedP values <0.05 were considered statistically significant.
Number of articles
Number of articles, mean cumulative impact factor (IF), mean population, mean cumulative IF per capita (p.c.) and mean IF between 1998 and 2007
Number of articles, 1998–2007
Cumulative IF, 1998–2007
Population (106), 1998–2007
Cumulative IF p.c. (IF/106), 1998–2007
The mean IF of published articles over all countries and years was 2.46 (range 1.52–2.93) (Table 2). The highest mean IFs were found for the Netherlands (2.93), Canada (2.80) and Switzerland (2.69).
Cumulative mean impact factors (IF) and gross domestic product (GDP), 1998–2006
Cumulative IF (109 US$), 1998–2006
GDP (IF/109 US$), 1998–2006
Cumulative IF/GDP, 1998–2006
Cumulative IF/health expenditure
Mean cumulative impact factor (IF) and health expenditures, 2001–2005
Cumulative IF, 2001–2005
Health expenditures (109 US$), 2001–2005
Cumulative IF/health expenditures (IF/109 US$), 2001–2005
Cumulative IF/public education expenditure
Mean cumulative impact factor (IF) and public education expenditure, 1998–2005
Cumulative IF, 1998–2005
Publ. ed. exp. (109 US$), 1998–2005
Cumulative IF/publ. ed. exp. (IF/109 US$), 1998–2005
Correlation of radiological research activity with socioeconomic factors
The current study demonstrates that radiological research activity increased over time in all countries. The overall number of articles published increased by +27% between 1998 and 2007. The cumulative IF doubled between 1998 and 2007. Some countries were able to increase their cumulative IF by several 100% (ranking leaders: Brazil, China, and South Korea).
Previously published studies have found that the USA falls behind in terms of both absolute numbers of published radiology papers  and also with regard to share of the total research output . However, based on our results, the USA published the largest number of articles. They continuously increased their cumulative IFs and made by far the greatest contribution to radiological research activity. The growth rates of the number of articles, cumulative IF, and cumulative IF per capita for the USA did not decrease after NIH funding stagnation in 2003  until 2007. On the contrary, the growth rates from 2003 to 2007 were even higher than between 1998 and 2003 (Figs. 1, 2).
However, the country ranking according to cumulative IF underwent a striking change after adjusting for population size and GDP. Small European countries (e.g. Switzerland, the Netherlands) led the rankings. This ranking has been previously shown for both radiology  and other disciplines [7, 10, 11]. Similar observations were made with regard to the standardisation according to health expenditure and public expenditure on education. The leading position of Israel in the ranking adjusted for health expenditure is at least partially explained by its low health expenditure per capita (average Israel: US $1,511 vs. average over all countries: $2,231) in combination with an above-average mean cumulative IF per capita (average Israel: 38.1/million vs. average over all countries: 29.2/million). A similar mechanism could be seen for the high ranking positions of Turkey with standardisation for health expenditure and public education expenditure; although for Turkey the high ratios can be explained by its low expenses.
The population-adjusted radiological research activity (cumulative IF per capita) correlated significantly with the per capita terms of the GDP, health expenditure and public expenditure on education. Multiple regression analysis demonstrated that public expenditure on education was the only parameter that was an independent predictor for the radiological research activity. GDP and health expenditure were highly correlated (Spearman rank correlation rho = 0.964). Potentially policy makers may use these data to argue for greater public education spending if research productivity is a goal.
It can be speculated that some health expenditure data given by the World Bank might have been calculated as a percentage of the GDP. A close relationship between increased GDP and high research activity has been found for other medical disciplines [8, 10, 12, 13, 17]. For ophthalmology, for example, Guerin et al. demonstrated a significant relationship between GDP per capita greater than $20,000 and the population-adjusted research output .
Obviously, productive medical research requires a strong and stable economy. Such a strong economy seems especially important in such medical disciplines as radiology, which requires large investment and has high running costs . Funding of research projects is another important aspect. A Canadian study  has shown that a significant relationship of national spending on research and English proficiency exists to publication output. These two variables explained approximately 70% of the variation in publication rate. Normalised for population size, English-speaking nations and certain European countries such as Denmark, the Netherlands, Switzerland, and Sweden had the highest rate of publication in the five highest ranked general medical journals (The New England Journal of Medicine,The Journal of the American Medical Association,The Annals of Internal Medicine,The British Medical Journal andThe Lancet).
There are several limitations to our study: Radiology papers published in non-radiological journals were not covered in this study. This is a substantial limitation of the study considering that a considerable number of radiological articles are published in non-radiology journals. Although we were not able to identify the radiological articles in non-radiology journals, we believe that our results in terms of relationships between research activity and the evaluated socioeconomic factors are probably not far from the real situation. The study was limited by considering only high-cited established journals over the last 10 years with the same length history of IFs. This may lead to an under-representation of very advanced topics for which journals have only recently been founded. Such journals are often not even indexed in the JCR but could have been relevant nevertheless . There is an ongoing debate about the use of the IF as an estimate of the quality of scientific research [29, 30]. However, there is no generally acknowledged better marker of publication quality at present . Another limitation was that the data on public education expenditure were incomplete for the study period. Therefore, comparability between results based on this parameter is not optimal.
Accepting these limitations, our study has shown that the United States had the highest radiological research activity for the period between 1998 and 2007, followed by Germany and the UK. The population-adjusted figures revealed the highest radiological research activity for Switzerland, followed by the Netherlands and Belgium. The radiological research activity demonstrates a close relationship to the GDP, health expenditure and public expenditure on education. However, of these three factors, only the latter factor independently predicts research activity.
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