Sixty-Five Years of Physical Therapy: Bibliometric Analysis of Research Publications From 1945 Through 2010

Discussion

This is the first study to report historical trends of published manuscripts in the journal of Physical Therapy over a 65-year time frame. Several bibliometric studies have been conducted in physical therapy^{4,17,20,22,25,27}; however, no study was identified that charted change in all 3 components of the research production process (producers, products, consumption) over more than a decade of publications and in relation to physical therapy. From 1945 through 2010, there were a number of changes in the characteristics of research producers, products, and consumption in Physical Therapy.

The trends in published manuscripts in Physical Therapy are clear; over the course of 65 years, more research (14 studies in 1945, 37 in 2010) was published by larger research concentrations from different affiliations (Collaboration Index: 3.4 in 1945, 8.5 in 2010), using higher research designs (Evidence Index: 0 in 1945, 2.8 in 2010), and greater quantitation (Quantitative Index: 0.38 in 1945, 1.3 in 2010) (Fig. 1). Several of the findings in the current study are similar to those reported by Coronado et al,⁴ despite the authors' use of different sampling frames (all journal issues published between 1980 and 2009 inclusive) and bibliometric measures (content analyses). For example, in both studies, there was a trend toward the use of higher research designs over the study period; however, the overall proportions of systematic reviews in the current study (8.1% of all published manuscripts in 2010) remained relatively low compared with other research designs used (eTable). In addition, both studies found most research published in Physical Therapy was conducted by authors affiliated with universities.

The move from “cottage” (small-scale, individual producers) to “industrial” (large-scale, highly organized producers) models of research production observed in the current study has also been reported in other health-related bibliometric literature in terms of research volume and the number of authors involved,^3,40 the location of international contributors,^41–43 sociodemographic determinants,^44,45 and the sophistication of research methods used and data reporting.²⁰

These findings are not surprising given the conceptual and technological advances that have occurred over the study period, making data collection and analysis process more sophisticated and dissemination easier. Collaboration among different authors, institutions, and countries has been facilitated by cheaper international travel, the widespread use of electronic media, a larger critical mass of researchers, and fierce competition in the research market for employment and funding opportunities. The rise of the concept of evidence-based practice in the early 1990s (marked by the founding of the Cochrane Collaboration in 1993)⁴⁶ has helped facilitate the evolution of research methods toward higher designs necessary to underpin treatment decision making, which subsequently informs the provision of effective and resource-efficient health services. Quantitative data analyses have been facilitated by advances in information technology, improved statistical software packages, and the development of standards for reporting research, such as CONSORT and PRISMA guidelines.^47,48 As CONSORT and PRISMA guidelines require detailed reporting of individual participant and study data (including recommending the use of tables and figures), they may in part account for the greater quantitation seen in articles published in Physical Therapy over time. Physical Therapy requires submitting authors to follow these statements and also limits topical or narrative reviews to clinical perspectives and invited commentaries. These and other journal policies may encourage the selective submittal of articles using higher research designs to Physical Therapy (compared with other physical therapy journals).

In the current study, the Evidence Index and Quantitative Index rose steadily but relatively modestly over the study period. The majority of the rise in the Evidence Index score occurred after 1990 and in the Quantitative Index after 1975, which mirrors some of the key research and computer-related developments (move toward experimental research designs, software to manage and access large data sets) and may assist in explaining the larger sample sizes used in research studies published later in the study period (Fig. 4). By contrast, the Collaboration Index in this study more than doubled and increased sharply after 2000 (Fig. 1). There are several plausible explanations for the publication patterns presented by Physical Therapy. The journal's current mission statement is explicit in aiming to engage and inspire an international readership. Therefore, it is possible that research with an international authorship has been increasingly submitted for consideration by Physical Therapy. As an alternate hypothesis, collaboration among more authors and among different institutions and countries may have actually grown due to factors such as the adoption in 1995 of declarations of principle and position statements by regions in the World Confederation for Physical Therapy (WCPT).^49,50 The most common locations (Canada, Australia, Taiwan, and Western Europe) of international collaborating authors of research over the study period, particularly in 2010, support this idea, given these countries (and others in which international authors who published in Physical Therapy resided) are well represented in the WCPT. The predominance of collaborating authors from highly industralized and developed countries could reflect increased competition in all markets, and especially the research market. However, it should be acknowledged that the rise of the Collaboration Index may simply reflect population growth, and specifically growth in the size of the overall health and physical therapy workforce, which would mean there would be more opportunities for collaboration.

Over the study period, a greater proportion of research was published in the journal by authors in the research sector (universities and research institutes) than by those involved in health service provision (hospitals, health services, and private practice). This trend also was reflected in the shifts seen in the topics of research articles (key word analyses), with growth in the use of key words reflecting research as opposed to decline in the use of key words relating to clinical areas of physical therapy (eg, acute care, clinical electrotherapy and wound management, sports). Key word analyses were conducted only over the most recent generation of the study period for which key words were available (1980–2010). The first 2 APTA sections (Education and Private Practice) were developed during the 1940s, with many others (the Neurology Section commenced in 1972, the Pediatrics and Sports Physical Therapy Sections in 1973, the Orthopaedic Section in 1974, and the Aquatic Physical Therapy Section around 1992) established in the years thereafter.³³ The evolving research focus of Physical Therapy also has been exemplified by the recent publication of various editorials.^51–55

Research being conducted predominantly in the area of and by authors in the research sector is most probably due to 2 important factors. First, research requires skills and infrastructure that health services may be unable to provide. These resource discrepancies may have become more pronounced as research has grown in its complexity and the scale on which it is conducted. Second, a changing workforce demographic may be at play. A greater number of research-skilled physical therapists and physical therapists who are skilled research consumers now exist. In a demographic profile of physical therapist members of APTA,⁵⁶ the proportion of respondents indicating the highest degree earned was a doctorate (either Doctor of Physical Therapy [DPT] or other doctorate) almost doubled over the last 5 years (21.4% of respondents in 2005, 41.2% in 2010). This finding may be due to the increased number of professional-level DPT programs offered in the United States.⁵⁷ If the increased proportion of physical therapists holding doctoral qualifications is predominantly due to graduates from entry-level DPT programs rather than graduate PhD programs (the proportion of APTA members with a PhD as their highest earned degree remained stable [6.2% in 2005, 6.7% in 2010]),⁵⁶ it seems unlikely that it would explain the growth in authors currently working within the academic setting. Physical therapy education programs have shifted from hospitals (health provider settings) to universities and research institutes (research sector) with tenure. This shift, combined with current accreditation standards requiring core full-time faculty members to demonstrate scholarly activity through research publications, means it is probably not surprising that the bulk of research published in Physical Therapy in recent years has been conducted in the education and research sectors.⁵⁸

Research across a greater cross-section of topics was published in Physical Therapy in 2010 (key words in 14 APTA sections) than in 1980 (key words in 10 APTA sections) (Tab. 2). This difference may have been due to the emergence of newer subspecialties within the physical therapy profession, the profile and relative membership of each section, and the opportunities for research to be published in section-specific publications rather than Physical Therapy.³³ The APTA sections vary significantly from one another in terms of their year of establishment, number of special interest groups (none in the Federal Physical Therapy Section, 10 in the Sports Physical Therapy Section), number of members (ranging from approximately 1,000 members in the Clinical Electrotherapy and Wound Management Section to more than 13,000 members in the Orthopaedic Section), and the nature and frequency of their associated publications (eg, a semiannual newsletter for the Research Section, 2 journals for the Sports Physical Therapy Section). These differences may account for the publication patterns seen in this study. It also is likely that shifting economic, political, and sociodemographic needs (toward research, geriatrics, older populations, and studies of both sexes) have helped shape and govern the research that is conducted and selected for publication. A mature profession and professional journal need to adapt to these changes, and rather than try to be “all things to all people” identify important and niche areas of research and foster and publish these studies preferentially.

In terms of the consumption of research published in Physical Therapy, there appeared to be a trend toward more recent publications receiving a greater number of citations, despite being published for and, therefore, accessible to its readership for less time (eFigure). This trend suggests that research consumption overall is increasing and that the research community is particularly interested in more recent publications. Curiously, there was a sharp fall in the number of citations of articles published after 2000 in the present study, which also was noted in the ISI Web of Science Journal Citation Reports Cited Journal Graph for Physical Therapy in 2004 and 2005 and after 2006.⁵⁹ Although the reasons for this decrease are unclear, 2005 was a period of editorial transition for Physical Therapy in terms of board membership and publication and review processes.⁶⁰

Bibliometric measures can be made at the research producer, product, and consumption levels and can provide valuable information regarding research performance. Bibliometric research is a way of describing intellectual activity and quantifying research performance over time and among different types of producers (eg, different institutions and professions). Performance indicators such as these are important, given there is increased competition in the research market among researchers and institutions for available resources and an accelerated drive toward evidence-based and cost-effective health care. Bibliometric studies are useful in describing the natural history of a profession or publication and can be used in benchmarking activities with and against other journals and disciplines or to evaluate the effectiveness of research initiatives.

It is important that a profession, or a professional journal, remain intrinsically “in tune” with its members and readership to respond to these factors and the changing tempo of the research market. Physical Therapy consumers may use the journal by citing published manuscripts or through general readership. Therefore, the total consumption of Physical Therapy by APTA members may not be reflected in traditional citation-based bibliometric indexes alone. More than 50% of current APTA members are employed in private or health system/hospital–based outpatient facilities⁵⁶ and are more likely to use research findings published in Physical Therapy in their clinical practice rather than through citation. Therefore, the degree of harmony between a professional journal and its target demographic (readership and members) may be able to be captured more completely with the use of more novel bibliometric indexes that can describe the research designs used, populations and topics studied, productivity of various research teams, and access and download rates of published manuscripts. It appears that over the last 65 years, Physical Therapy has been in concert with many of these factors and has endeavored to remain true to the goals of facilitating contact among researchers and countries. It is likely that these publication trends in Physical Therapy, and in general, will continue and escalate in the future.