# Bibliometric Study of the Comorbidity of Pain and Depression Research

Authors: Xue-Qiang Wang; Meng-Si Peng; Lin-Man Weng; Yi-Li Zheng; Zhi-Jie Zhang; Pei-Jie Chen
Journal: Neural Plasticity
 (2019)

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## Abstract

Background. Comorbid pain and depression occur with high prevalence in clinical observations, and published academic journals about them have been increasing in number over time. However, few studies used the bibliometric method to analyze the general aspects of scientific researches on the comorbidity of pain and depression. The aim of this study is to systematically provide global scientific research in the comorbidity of pain and depression from 1980 to 2018. Methods. The published papers were searched between 1980 and 2018 in Web of Science. Publications related to comorbid pain and depression research were included. The language was restricted to English, and no species limitations were specified. Results. A total of 2,519 papers met the inclusion criteria in our study. The results revealed that the publications had a significant growth over time in the comorbidity of pain and depression research (P<0.001) by linear regression analyses. The United States had the largest number of publications and citations and the highest value of H-index. According to subject categories of Web of Science, research areas of the 2,519 papers mainly focused on clinical neurology (28.78%), neurosciences (22.9%), and psychiatry (22.23%). In accordance with types of pain, headache (19.09%) was the most popular topic in the included papers on comorbid pain and depression research. Conclusions. The findings provide useful information for pain and depression researchers to detect new areas related to collaborators, cooperative institutions, popular topics, and research frontiers.


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## Body

## 1. Introduction

Pain is the most pervasive physical symptom in primary care, which affects physical and emotive functions, deteriorates the quality of life, and reduces the ability to work [1–4]. The prevalence of chronic pain has been estimated to be as high as 40% in the United States [5]. The most common types of pain syndromes [6–8] include headache, low back pain, fibromyalgia, neuropathic pain, arthritis, cancer, and postsurgical pain. The total cost of pain has been calculated to be as high as 3% of the gross domestic product of European countries, which is larger than the cost of cancer or heart disease [9]. Depression is the most common psychological symptom and is a major public health concern in primary care [10, 11]. The prevalence of depressive symptoms or depression among medical students from 43 countries has been reported to be 27.2% [12], and the lifetime prevalence of depression in 30 countries has been calculated to be 10.8% [13]. In Japan, the total cost of depression among adults was estimated to be ¥2.0 trillion in 2005 [14].Comorbid pain and depression occur with high prevalence in clinical observations, as high as 60% [4]. A number of studies have reported that antidepressant drugs have been used to treat pain since the 1960s [4, 15]. Pain intensity is aggravated by increasing levels of depression [16]. Although the neurobiological mechanisms of the interaction between pain and depression are unclear, human neuroimaging studies indicate that depression can influence changes in multiple brain regions including those related to pain processing and perception [17, 18].While research on comorbid pain and depression is widely available worldwide, relatively few studies use bibliometric methods to analyze the general aspects of this research topic. Bibliometric studies are extensively used to determine trends of scientific research and involve quantitative analysis of published studies [19, 20]. This type of study could offer readers quantitative information on distribution by country, institution, author, and journal in a specific field. Over the last 10 years, bibliometric studies have been used to analyze scientific research in different areas, such as long noncoding RNA [21], paediatric pain [22], cancer rehabilitation [23], childhood immunization [24], eye disease [25], and drug delivery [26], worldwide.To address the shortage of quantitative analysis of comorbid pain and depression research, the aim of this study is to systematically provide global scientific research in this field from 1980 to 2018. We used CiteSpace V (Drexel University, Philadelphia, United States) to perform a bibliometric study in Web of Science Core Collection, which is a tool frequently used to assess the trends in the global scientific research [27]. In this study, global scientific research on comorbid pain and depression includes the number of published papers, types of pain, distribution and collaborations between authors/institutions/countries, a citation burst analysis of keywords, cocitation analysis of authors and references.


## 2. Methods

### 2.1. Sources of the Data

The published papers were searched in the recent forty years (from 1980 to 2018). We downloaded and extracted the publications from Science Citation Index Expanded (SCI-Expanded) of Web of Science. The following terms were searched: Title=(pain∗ or headache∗ or migraine∗ or head-ache∗ or “head ache∗” or cephalalgi∗ or “abdominal ache∗” or fibromyalg∗ or “tummy ache∗” or “stomach ache∗” or “belly ache∗” or ear-ache∗ or earache∗ or tooth-ache∗ or toothache∗ or odontalgi∗ or neuralgi∗ or cervicodyn∗ or analg∗ or nocicept∗ or hyperalg∗ or hypoalg∗ or radiculalg∗ or colic or arthralg∗ or causalg∗ or maldyn∗ or eudyn∗ or ophthalmodyn∗ or cephalalg∗ or dysmenorrh∗ or sciatic∗ or otalg∗ or brachialg∗) and Title=(depression or depressions or depressed or despondent or gloomy or depressive).


### 2.2. Inclusion Criteria

We included articles, reviews, letters, and editorial materials published in different academic journals. Meeting abstracts, conference presentations, book reviews, news items, and corrections were excluded. Publications related to comorbid pain and depression research were included. The language was restricted to English, and no species limitations were specified.


### 2.3. Data Extraction

The two authors (Lin-Man Weng and Xue-Qiang Wang) extracted the publications and used EndNote (EndNote X7, Bld 7072, Thomson Research Soft, Stamford) and Microsoft Excel 2016 to perform the downloaded published studies. We extracted and recorded pertinent information, such as publication count, journal, institution, country, and citation frequency, as bibliometric indicators. TheH-index is recognized as a measurement of the papers’ citation frequency for academic journals or researchers. For example, the H-index is that an academic journal or researcher has H published papers which have at least H citation times per paper (If the H-index of one researcher is 10, that means that he had published at least 10 papers and each of these 10 papers had been cited at least 10 times.) [28]. Furthermore, these included studies that were classified into the following categories: (1) single- or multiple-authored publications (authors≥2); (2) Web of Science subject category. We would select and assess the top 20 subject categories of Web of Science categories according to the included studies. Every paper or journal is assigned to at least one Web of Science category in Web of Science core collection. Thus, the sum of publications could be more than 2,519. Research areas were classified into five broad categories in Web of Science categories, and the five broad categories included 225 subject categories [29], such as anesthesiology, neurosciences, and psychiatry; (3) types of pain. We would choose and analyze the top ten types of pain (such as headache and low back pain) according to the included studies. Because some papers exceeded one type of pain, the sum of publications could be more than 2,519. For example, the paper by Gesztelyi and Bereczki included headaches and low back pain [30].


### 2.4. Statistical Methods

CiteSpace V and Microsoft Excel 2016 were used to (1) analyze the distribution by journals, years, countries, institutions, and authors, (2) assess the collaborations between countries, institutions, and authors, (3) perform analysis of citations and H-index, and (4) conduct analysis of reference and keywords. In addition, we calculated a percentage score each year for some categories (all the articles were divided into different categories, the number of publications per year of one category divided by the total number of publications of this category), such as single-authored publications and multiple-authored publications, subject categories of Web of Science, and types of pain. To assess whether the percentage statistically decreased or increased over time, the linear regression analyses were conducted with every respective category as the dependent variable and the year as the independent variable. The statistical analyses were performed with IBM SPSS Statistics 22.0 software (SPSS Inc., Chicago, USA). AP value less than 0.05 was considered as statistical significance.


## 2.1. Sources of the Data

The published papers were searched in the recent forty years (from 1980 to 2018). We downloaded and extracted the publications from Science Citation Index Expanded (SCI-Expanded) of Web of Science. The following terms were searched: Title=(pain∗ or headache∗ or migraine∗ or head-ache∗ or “head ache∗” or cephalalgi∗ or “abdominal ache∗” or fibromyalg∗ or “tummy ache∗” or “stomach ache∗” or “belly ache∗” or ear-ache∗ or earache∗ or tooth-ache∗ or toothache∗ or odontalgi∗ or neuralgi∗ or cervicodyn∗ or analg∗ or nocicept∗ or hyperalg∗ or hypoalg∗ or radiculalg∗ or colic or arthralg∗ or causalg∗ or maldyn∗ or eudyn∗ or ophthalmodyn∗ or cephalalg∗ or dysmenorrh∗ or sciatic∗ or otalg∗ or brachialg∗) and Title=(depression or depressions or depressed or despondent or gloomy or depressive).


## 2.2. Inclusion Criteria

We included articles, reviews, letters, and editorial materials published in different academic journals. Meeting abstracts, conference presentations, book reviews, news items, and corrections were excluded. Publications related to comorbid pain and depression research were included. The language was restricted to English, and no species limitations were specified.


## 2.3. Data Extraction

The two authors (Lin-Man Weng and Xue-Qiang Wang) extracted the publications and used EndNote (EndNote X7, Bld 7072, Thomson Research Soft, Stamford) and Microsoft Excel 2016 to perform the downloaded published studies. We extracted and recorded pertinent information, such as publication count, journal, institution, country, and citation frequency, as bibliometric indicators. TheH-index is recognized as a measurement of the papers’ citation frequency for academic journals or researchers. For example, the H-index is that an academic journal or researcher has H published papers which have at least H citation times per paper (If the H-index of one researcher is 10, that means that he had published at least 10 papers and each of these 10 papers had been cited at least 10 times.) [28]. Furthermore, these included studies that were classified into the following categories: (1) single- or multiple-authored publications (authors≥2); (2) Web of Science subject category. We would select and assess the top 20 subject categories of Web of Science categories according to the included studies. Every paper or journal is assigned to at least one Web of Science category in Web of Science core collection. Thus, the sum of publications could be more than 2,519. Research areas were classified into five broad categories in Web of Science categories, and the five broad categories included 225 subject categories [29], such as anesthesiology, neurosciences, and psychiatry; (3) types of pain. We would choose and analyze the top ten types of pain (such as headache and low back pain) according to the included studies. Because some papers exceeded one type of pain, the sum of publications could be more than 2,519. For example, the paper by Gesztelyi and Bereczki included headaches and low back pain [30].


## 2.4. Statistical Methods

CiteSpace V and Microsoft Excel 2016 were used to (1) analyze the distribution by journals, years, countries, institutions, and authors, (2) assess the collaborations between countries, institutions, and authors, (3) perform analysis of citations and H-index, and (4) conduct analysis of reference and keywords. In addition, we calculated a percentage score each year for some categories (all the articles were divided into different categories, the number of publications per year of one category divided by the total number of publications of this category), such as single-authored publications and multiple-authored publications, subject categories of Web of Science, and types of pain. To assess whether the percentage statistically decreased or increased over time, the linear regression analyses were conducted with every respective category as the dependent variable and the year as the independent variable. The statistical analyses were performed with IBM SPSS Statistics 22.0 software (SPSS Inc., Chicago, USA). AP value less than 0.05 was considered as statistical significance.


## 3. Results

### 3.1. Publication Outputs and Growth Trends

A total of 2,519 papers met the inclusion criteria; 1,264 papers (meeting abstracts, proceedings papers, notes, corrections, book reviews, and news items) and 151 non-English papers were excluded (Supplementary Figure1). The overall trend of publications increased from five publications in 1980 to 179 publications in 2018 (Figure 1(a)). The results of linear regression analyses showed that the percentages had a significant increase over time in the recent forty years (t=11.37, P<0.001). All papers related to comorbid pain and depression research were cited 74,746 times (29.67 times per year, H-index 121), and the percentages had a significant increase over time (t=12.47, P<0.001) (Figure 1(b)). Among the eight 5 years (1980-1984, 1985-1989, 1990-1994, 1995-1999, 2000-2004, 2005-2009, 2010-2014, and 2014-2018), 2005-2009 had the largest number of citations (17,528) and the highest value of H-index (66), 2000-2004 had the largest number of citations per paper (69.58), 2010-2014 had the largest number of citations (2429) in 2018, and 2014-2018 had the largest number of publications (858) and open access papers (335) (Figure 2).Figure 1
Number of publications and citations. (a) The number of annual publications on pain and depression research from 1980 to 2018; (b) the number of annual citations on pain and depression research from 1980 to 2018.
(a)
(b)Figure 2
Number of papers, citations, citations per paper, open access paper,H-index, and citations in 2018 for each 5-year time period.


### 3.2. Distribution by Journals

The 2,519 papers on comorbid pain and depression research were published in 251 academic journals (Supplementary Table1). Among the top 20 journals by the number of publications (Table 1), Pain, in which impact factor (IF) 2017 was 5.559, contributed to the most publications on comorbid pain and depression research (136 publications, 5.39%), followed by Clinical Journal of Pain (IF 2017, 3.209; 57 publications; 2.26%), Headache (IF 2017, 3.091; 57 publications; 2.26%), and Cephalalgia (IF 2017, 3.886; 50 publications; 1.98%). The top 20 journals contributed to 29.37% of the total number of publications. The highest value of H-index was with Pain (97), the largest number of citations per paper was with Psychosomatic Medicine (IF 2017, 3.81), and the highest value of IF 2017 was with Anesthesiology (IF 2017, 6.523). In journal IF quartile of Web of Science, 55% of journals were Q1 (Q1 stands for the top 25% of the IF distribution) and 40% of journals were Q2 (Q2 stands for between top 50% and top 25% of the IF distribution) among the 20 journals.Table 1
The top 20 journals of origin of papers in the pain and depression research.
Journals
Papers
Citations (WoS)
Citations per paper
Open access
WoS categories
IF 2017
Quartile
H-index
Pain
136
9036
66.44
18
Anesthesiology; Clinical Neurology; Neurosciences
5.559
Q1; Q1; Q1
56
Clinical Journal of Pain
57
2465
43.25
4
Anesthesiology; Clinical Neurology
3.209
Q2; Q2
23
Headache
57
1671
29.32
10
Clinical Neurology
3.091
Q2
26
Cephalalgia
50
1130
22.60
4
Clinical Neurology; Neurosciences
3.886
Q1; Q2
18
Pain Medicine
47
1022
21.74
45
Anesthesiology; Medicine, General, & Internal
2.782
Q2; Q1
18
Journal of Pain
43
1703
39.60
6
Clinical Neurology; Neurosciences
4.859
Q1; Q1
22
Journal of Affective Disorders
41
1119
27.29
3
Clinical Neurology; Psychiatry
3.786
Q1; Q1
21
European Journal of Pain
40
826
20.65
6
Anesthesiology; Clinical Neurology; Neurosciences
2.991
Q2; Q2; Q3
17
Journal of Clinical Psychiatry
28
1342
47.93
1
Psychiatry; Psychology, Clinical
4.247
Q1; Q1; Q1
18
Journal of Psychosomatic Research
27
1089
40.33
1
Psychiatry
2.947
Q2
16
Journal of Headache and Pain
26
377
14.50
26
Clinical Neurology; Neurosciences
3.403
Q2; Q2
11
General Hospital Psychiatry
25
706
28.24
10
Psychiatry
2.989
Q2
15
Psychosomatic Medicine
24
1719
71.63
5
Psychiatry; Psychology; Psychology, Multidisciplinary
3.81
Q1; Q1; Q1
20
PLoS One
24
274
11.42
24
Multidisciplinary Sciences
2.776
Q1
9
Psychosomatics
23
693
30.13
2
Psychiatry; Psychology
2.534
Q2; Q2
12
Journal of Pain and Symptom Management
22
975
44.32
3
Clinical Neurology; Health Care Sciences & Services; Medicine, General, & Internal
2.498
Q2; Q1; Q1
16
Anesthesia and Analgesia
19
493
25.95
3
Anesthesiology
3.463
Q1
11
Anesthesiology
18
625
34.72
3
Anesthesiology
6.523
Q1
10
Journal of Nervous and Mental Disease
17
799
47
0
Clinical Neurology; Psychiatry
2.776
Q3; Q3
10
Journal of Rheumatology
16
891
55.69
0
Rheumatology
3.47
Q2
16A dual-map overlay of journals is presented in Figure3. In the dual-map, the map of the citing journals is on the left and the map of the cited journals is on the right. The disciplines included in the journals are shown as labels in the dual map. The lines are considered citation connections, beginning from the citing journals to the cited journals. The dual-map overlay shows that the majority of papers were published in neurology, sports, and ophthalmology journals and these journals mostly cited journals from psychology, education, and social areas.Figure 3
The dual-map overlay of journals related to pain and depression research.


### 3.3. Subject Categories of Web of Science

Research areas of the 2,519 papers on comorbid pain and depression research were assigned to 55 subject categories of Web of Science. In top 20 subject categories (Figure4), according to the number of publications, Clinical Neurology had the largest number of publications (725), citations (27,087), and open access papers (170) and the highest value of H-index (80). The Psychology Multidisciplinary subject category had the largest number of citations per paper (47.89). Moreover, the results of linear regression analyses showed that the percentages of publication count per year had a statistical increase over time (P<0.01) in the top 20 subject categories (Clinical Neurology, Neurosciences, Psychiatry, Anesthesiology, Medicine General Internal, Psychology Clinical, Pharmacology Pharmacy, Rheumatology, Psychology, Rehabilitation, Public Environmental Occupational Health, Orthopedics, Psychology Multidisciplinary, Health Care Sciences Services, Nursing, Geriatrics Gerontology, Gerontology, Medicine Research Experimental, Multidisciplinary Sciences, and Surgery).Figure 4
The number of papers, citations, citations per paper, open access papers, and H-index of the top 20 subject categories of Web of Science.


### 3.4. Types of Pain

As shown in Figure5, according to the number of publications, headache (19.09%) was the most popular topic in the included papers on comorbid pain and depression research, followed by low back pain, animal models of pain, and fibromyalgia. Among the top 10 types of pain, headache had the largest number of publications (481), citations (15,674), and open access papers (135) and the highest value of H-index (59). Arthritis had the largest number of citations per paper (45.49). In addition, the results showed that the percentages of publication count per year had a significant increase over time (P<0.01) in headache, low back pain, animal models of pain, fibromyalgia, neuropathic pain, arthritis, cancer pain, postsurgical pain, visceral pain, and neck pain.Figure 5
The number of papers, citations, citations per paper, open access papers and H-index of the top 10 types of pain.


### 3.5. Distribution by Countries and Institutions

The 2,519 papers on comorbid pain and depression research were contributed by 75 countries/territories (Supplementary Table2). Figure 6 shows the top 10 countries/territories by quantity of papers, showed as sums of paper fractions. The United States had the largest number of publications (1,105), citations (44,490), and open access papers (342) and the highest value of H-index (102). The Netherlands had the largest number of citations per paper (40.37). In relation to the top 10 countries that contributed to comorbid pain and depression research, USA led the first research echelon, followed by the England (178), Canada (156), and Germany (139). There were extensive collaborations between countries/territories (Figure 7(a)). In accordance with the number of published papers, the overview of all countries was presented in world map (Figure 8).Figure 6
The number of papers, citations, citations per paper, open access papers, andH-index of the top 10 countries.Figure 7
The analysis of countries and institutions. (a) Network map of countries/territories engaged in pain and depression research; (b) network map of institutions engaged in pain and depression research.
(a)
(b)Figure 8
World map of total country output based on pain and depression research.A total of 1,884 institutions contributed to the publications on comorbid pain and depression research (Supplementary Table3). The top 10 institutions (Supplementary Figure 2) contributed to 30.77% of the total number of publications. The University of California System had the largest number of publications (108), University of Washington had the largest number of citations (5,680), Eli Lilly had the largest number of citations per paper (108), and Harvard University had the largest number of open access papers (45) and the highest value of H-index (37). Figure 7(b) showed the network map of institutions engaged in pain and depression research.


### 3.6. Distribution by Authors

A total of 8,771 authors contributed to the total number of publications. The network map in Figure9 outlines the cooperation between authors. Amongst the authors who had the most publications (Table 2), Kroenke K ranked the first with 35 publications, followed by Bair MJ with 21 publications, Negus SS with 19 publications, and Wang SJ with 19 publications. Amongst the top 10 cocited authors (Table 2), Bair MJ with 447 citations, followed by Beck AT with 403 citations, Kroenke K with 337 citations, and Turk DC with 236 citations were the most popular. Figure 10 indicates that the percentages of multiple-author papers (≥2) increased from 65.66% in 1980–1984 to 96.27% in 2014–2018. The linear regression results revealed that the percentage of papers with multiple authors significantly increased and that with a single author significantly decreased (t=11.76, P<0.001).Figure 9
The analysis of authors. Network map of active authors that contributed to pain and depression research.Table 2
The top 10 authors, cocited authors, and cocited references in the pain and depression research.
Author
Published articles
Cocited author
Cited times
Cocited reference
Cited times
Kroenke K
35
Bair MJ
447
Bair MJ, 2003, Arch Intern Med, V163, P2433
154
Bair MJ
21
Beck AT
403
Bair MJ, 2004, Psychosom Med, V66, P17
72
Negus SS
19
Kroenke K
337
Ohayon MM, 2003, Arch Gen Psychiat, V60, P39
72
Wang SJ
19
Turk DC
236
Kroenke K, 2011, J Pain, V12, P964
61
Wu JW
18
Fishbain DA
228
Blumer D, 1982, J Nerv Ment Dis, V170, P381
46
Ferrari MD
15
Wolfe F
223
Romano JM, 1985, Psychol Bull, V97, P18
46
Hung CI
15
Vonkorff M
202
Arnow BA, 2006, Psychosom Med, V68, P262
44
Liu CY
15
∗∗American Psychiatric Association
199
Karp JF, 2005, J Clin Psychiat, V66, P591
40
Arnold LM
13
Radloff LS
195
Currie SR, 2004, Pain, V107, P54
38
Ayata C
13
Breslau N
182
Demyttenaere K, 2006, J Affect Disorders, V92, P185
37Figure 10
Trends in the percentage of single- vs multiple-authored articles per 5 years.


### 3.7. Analysis of References

Analysis of references was regarded as an important indicator in bibliometric study. The scientific relevance of the published papers was presented in the cocitation map of references (Figure11). The modularity Q score was 0.8897 (higher than 0.5), which indicated that the network was reasonably distributed to loosely coupled clusters. All clusters were traced by index terms extracted from the references. The “rehabilitation outcome” was labeled as the largest cluster #0, followed by “home care” as the second largest cluster #1, “pain comorbidity” as the third largest cluster #2, and “depressive disease.” As shown in Figure 11, the top 23 clusters were showed in a timeline view.Figure 11
The analysis of references. Cocitation map (timeline view) of references from publications on to pain and depression research.


### 3.8. Analysis of Keywords

The keywords of the 2,519 published papers were extracted by CiteSpace V. Figure12 reveals the top 47 keywords with the strongest citation bursts. Keywords with the strongest citation bursts beginning in 1991 were as follows: “disease,” “illness,” “chronic pain,” and “inventory.” The top 47 keywords by the end of 2018 included “older adult” (2014–2018), “validity” (2015–2018), “impact” (2016–2018), and “association” (2016–2018).Figure 12
The keywords with the strongest citation bursts of publications on pain and depression research.


### 3.9. Characteristics of Top 10 Papers Cited Most Frequently

Table3 showed the top ten papers on comorbid pain and depression research with the most citation frequency. The top 10 papers contributed to 7.81% (5,831 citations) of the total number of citations. The article by Bair et al. [31] published in 2003 was the most cited (1,442 citations) paper, and the article is entitled “Depression and pain comorbidity-a literature review.” published in Archives of Internal Medicine. Among the top 10 papers, five [31–35] were published in journals with impact factor≥10 (Archives of Internal Medicine, Brain, Psychological Bulletin and Neuron), two [36, 37] in journals with 5≤impactfactor<10 (Neurology, Arthritis & Rheumatology), two [38, 39] in journals with 3≤impactfactor<5 (Clinical Journal of Pain, Journal of Pain), and one [40] journal with 1≤impactfactor<3 (The Journal of Nervous and Mental Disease).Table 3
The top 10 papers with the most citation frequency in the pain and depression research.
Title
First author
Journal
Impact factor
Year
Citations (WoS)
WoS categories
Category ranking
Depression and pain comorbidity-a literature review
Bair MJ
Archives of Internal Medicine
17.33IF 2014
2003
1442
Medicine, General, & Internal
6/154
Pathophysiology of the migraine aura. The spreading depression theory
Lauritzen M.
Brain
10.848
1994
785
Clinical Neurology; Neurosciences
6/197; 13/261
Chronic pain-associated depression: antecedent or consequence of chronic pain? A review
Fishbain DA
Clinical Journal of Pain
3.209
1997
585
Anesthesiology; Clinical Neurology
11/31; 69/197
Chronic pain and depression: does the evidence support a relationship?
Romano JM
Psychological Bulletin
13.25
1985
513
Psychology; Psychology, Multidisciplinary
3/78; 4/135
Amitriptyline relieves diabetic neuropathy pain in patients with normal or depressed mood
Max MB
Neurology
8.055
1987
462
Clinical Neurology
13/197
Chronic pain as a variant of depressive disease: the pain-prone disorder
Blumer D
The Journal of Nervous and Mental Disease
1.94
1982
460
Clinical Neurology; Psychiatry
134/197; 89/142
Explaining high rates of depression in chronic pain: a diathesis-stress framework
Banks SM
Psychological Bulletin
13.25
1996
434
Psychology; Psychology, Multidisciplinary
3/78; 4/135
A double-blind, multicenter trial comparing duloxetine with placebo in the treatment of fibromyalgia patients with or without major depressive disorder
Arnold LM
Arthritis & Rheumatology
7.379
2004
392
Rheumatology
1/22
Common chronic pain conditions in developed and developing countries: gender and age differences and comorbidity with depression-anxiety disorders
Tsang A
Journal of Pain
4.859
2008
382
Clinical Neurology; Neurosciences
27/197; 51/261
A Cacna1a knockin migraine mouse model with increased susceptibility to cortical spreading depression
van den Maagdenberg AMJM
Neuron
14.319
2004
376
Neurosciences
7/261


## 3.1. Publication Outputs and Growth Trends

A total of 2,519 papers met the inclusion criteria; 1,264 papers (meeting abstracts, proceedings papers, notes, corrections, book reviews, and news items) and 151 non-English papers were excluded (Supplementary Figure1). The overall trend of publications increased from five publications in 1980 to 179 publications in 2018 (Figure 1(a)). The results of linear regression analyses showed that the percentages had a significant increase over time in the recent forty years (t=11.37, P<0.001). All papers related to comorbid pain and depression research were cited 74,746 times (29.67 times per year, H-index 121), and the percentages had a significant increase over time (t=12.47, P<0.001) (Figure 1(b)). Among the eight 5 years (1980-1984, 1985-1989, 1990-1994, 1995-1999, 2000-2004, 2005-2009, 2010-2014, and 2014-2018), 2005-2009 had the largest number of citations (17,528) and the highest value of H-index (66), 2000-2004 had the largest number of citations per paper (69.58), 2010-2014 had the largest number of citations (2429) in 2018, and 2014-2018 had the largest number of publications (858) and open access papers (335) (Figure 2).Figure 1
Number of publications and citations. (a) The number of annual publications on pain and depression research from 1980 to 2018; (b) the number of annual citations on pain and depression research from 1980 to 2018.
(a)
(b)Figure 2
Number of papers, citations, citations per paper, open access paper,H-index, and citations in 2018 for each 5-year time period.


## 3.2. Distribution by Journals

The 2,519 papers on comorbid pain and depression research were published in 251 academic journals (Supplementary Table1). Among the top 20 journals by the number of publications (Table 1), Pain, in which impact factor (IF) 2017 was 5.559, contributed to the most publications on comorbid pain and depression research (136 publications, 5.39%), followed by Clinical Journal of Pain (IF 2017, 3.209; 57 publications; 2.26%), Headache (IF 2017, 3.091; 57 publications; 2.26%), and Cephalalgia (IF 2017, 3.886; 50 publications; 1.98%). The top 20 journals contributed to 29.37% of the total number of publications. The highest value of H-index was with Pain (97), the largest number of citations per paper was with Psychosomatic Medicine (IF 2017, 3.81), and the highest value of IF 2017 was with Anesthesiology (IF 2017, 6.523). In journal IF quartile of Web of Science, 55% of journals were Q1 (Q1 stands for the top 25% of the IF distribution) and 40% of journals were Q2 (Q2 stands for between top 50% and top 25% of the IF distribution) among the 20 journals.Table 1
The top 20 journals of origin of papers in the pain and depression research.
Journals
Papers
Citations (WoS)
Citations per paper
Open access
WoS categories
IF 2017
Quartile
H-index
Pain
136
9036
66.44
18
Anesthesiology; Clinical Neurology; Neurosciences
5.559
Q1; Q1; Q1
56
Clinical Journal of Pain
57
2465
43.25
4
Anesthesiology; Clinical Neurology
3.209
Q2; Q2
23
Headache
57
1671
29.32
10
Clinical Neurology
3.091
Q2
26
Cephalalgia
50
1130
22.60
4
Clinical Neurology; Neurosciences
3.886
Q1; Q2
18
Pain Medicine
47
1022
21.74
45
Anesthesiology; Medicine, General, & Internal
2.782
Q2; Q1
18
Journal of Pain
43
1703
39.60
6
Clinical Neurology; Neurosciences
4.859
Q1; Q1
22
Journal of Affective Disorders
41
1119
27.29
3
Clinical Neurology; Psychiatry
3.786
Q1; Q1
21
European Journal of Pain
40
826
20.65
6
Anesthesiology; Clinical Neurology; Neurosciences
2.991
Q2; Q2; Q3
17
Journal of Clinical Psychiatry
28
1342
47.93
1
Psychiatry; Psychology, Clinical
4.247
Q1; Q1; Q1
18
Journal of Psychosomatic Research
27
1089
40.33
1
Psychiatry
2.947
Q2
16
Journal of Headache and Pain
26
377
14.50
26
Clinical Neurology; Neurosciences
3.403
Q2; Q2
11
General Hospital Psychiatry
25
706
28.24
10
Psychiatry
2.989
Q2
15
Psychosomatic Medicine
24
1719
71.63
5
Psychiatry; Psychology; Psychology, Multidisciplinary
3.81
Q1; Q1; Q1
20
PLoS One
24
274
11.42
24
Multidisciplinary Sciences
2.776
Q1
9
Psychosomatics
23
693
30.13
2
Psychiatry; Psychology
2.534
Q2; Q2
12
Journal of Pain and Symptom Management
22
975
44.32
3
Clinical Neurology; Health Care Sciences & Services; Medicine, General, & Internal
2.498
Q2; Q1; Q1
16
Anesthesia and Analgesia
19
493
25.95
3
Anesthesiology
3.463
Q1
11
Anesthesiology
18
625
34.72
3
Anesthesiology
6.523
Q1
10
Journal of Nervous and Mental Disease
17
799
47
0
Clinical Neurology; Psychiatry
2.776
Q3; Q3
10
Journal of Rheumatology
16
891
55.69
0
Rheumatology
3.47
Q2
16A dual-map overlay of journals is presented in Figure3. In the dual-map, the map of the citing journals is on the left and the map of the cited journals is on the right. The disciplines included in the journals are shown as labels in the dual map. The lines are considered citation connections, beginning from the citing journals to the cited journals. The dual-map overlay shows that the majority of papers were published in neurology, sports, and ophthalmology journals and these journals mostly cited journals from psychology, education, and social areas.Figure 3
The dual-map overlay of journals related to pain and depression research.


## 3.3. Subject Categories of Web of Science

Research areas of the 2,519 papers on comorbid pain and depression research were assigned to 55 subject categories of Web of Science. In top 20 subject categories (Figure4), according to the number of publications, Clinical Neurology had the largest number of publications (725), citations (27,087), and open access papers (170) and the highest value of H-index (80). The Psychology Multidisciplinary subject category had the largest number of citations per paper (47.89). Moreover, the results of linear regression analyses showed that the percentages of publication count per year had a statistical increase over time (P<0.01) in the top 20 subject categories (Clinical Neurology, Neurosciences, Psychiatry, Anesthesiology, Medicine General Internal, Psychology Clinical, Pharmacology Pharmacy, Rheumatology, Psychology, Rehabilitation, Public Environmental Occupational Health, Orthopedics, Psychology Multidisciplinary, Health Care Sciences Services, Nursing, Geriatrics Gerontology, Gerontology, Medicine Research Experimental, Multidisciplinary Sciences, and Surgery).Figure 4
The number of papers, citations, citations per paper, open access papers, and H-index of the top 20 subject categories of Web of Science.


## 3.4. Types of Pain

As shown in Figure5, according to the number of publications, headache (19.09%) was the most popular topic in the included papers on comorbid pain and depression research, followed by low back pain, animal models of pain, and fibromyalgia. Among the top 10 types of pain, headache had the largest number of publications (481), citations (15,674), and open access papers (135) and the highest value of H-index (59). Arthritis had the largest number of citations per paper (45.49). In addition, the results showed that the percentages of publication count per year had a significant increase over time (P<0.01) in headache, low back pain, animal models of pain, fibromyalgia, neuropathic pain, arthritis, cancer pain, postsurgical pain, visceral pain, and neck pain.Figure 5
The number of papers, citations, citations per paper, open access papers and H-index of the top 10 types of pain.


## 3.5. Distribution by Countries and Institutions

The 2,519 papers on comorbid pain and depression research were contributed by 75 countries/territories (Supplementary Table2). Figure 6 shows the top 10 countries/territories by quantity of papers, showed as sums of paper fractions. The United States had the largest number of publications (1,105), citations (44,490), and open access papers (342) and the highest value of H-index (102). The Netherlands had the largest number of citations per paper (40.37). In relation to the top 10 countries that contributed to comorbid pain and depression research, USA led the first research echelon, followed by the England (178), Canada (156), and Germany (139). There were extensive collaborations between countries/territories (Figure 7(a)). In accordance with the number of published papers, the overview of all countries was presented in world map (Figure 8).Figure 6
The number of papers, citations, citations per paper, open access papers, andH-index of the top 10 countries.Figure 7
The analysis of countries and institutions. (a) Network map of countries/territories engaged in pain and depression research; (b) network map of institutions engaged in pain and depression research.
(a)
(b)Figure 8
World map of total country output based on pain and depression research.A total of 1,884 institutions contributed to the publications on comorbid pain and depression research (Supplementary Table3). The top 10 institutions (Supplementary Figure 2) contributed to 30.77% of the total number of publications. The University of California System had the largest number of publications (108), University of Washington had the largest number of citations (5,680), Eli Lilly had the largest number of citations per paper (108), and Harvard University had the largest number of open access papers (45) and the highest value of H-index (37). Figure 7(b) showed the network map of institutions engaged in pain and depression research.


## 3.6. Distribution by Authors

A total of 8,771 authors contributed to the total number of publications. The network map in Figure9 outlines the cooperation between authors. Amongst the authors who had the most publications (Table 2), Kroenke K ranked the first with 35 publications, followed by Bair MJ with 21 publications, Negus SS with 19 publications, and Wang SJ with 19 publications. Amongst the top 10 cocited authors (Table 2), Bair MJ with 447 citations, followed by Beck AT with 403 citations, Kroenke K with 337 citations, and Turk DC with 236 citations were the most popular. Figure 10 indicates that the percentages of multiple-author papers (≥2) increased from 65.66% in 1980–1984 to 96.27% in 2014–2018. The linear regression results revealed that the percentage of papers with multiple authors significantly increased and that with a single author significantly decreased (t=11.76, P<0.001).Figure 9
The analysis of authors. Network map of active authors that contributed to pain and depression research.Table 2
The top 10 authors, cocited authors, and cocited references in the pain and depression research.
Author
Published articles
Cocited author
Cited times
Cocited reference
Cited times
Kroenke K
35
Bair MJ
447
Bair MJ, 2003, Arch Intern Med, V163, P2433
154
Bair MJ
21
Beck AT
403
Bair MJ, 2004, Psychosom Med, V66, P17
72
Negus SS
19
Kroenke K
337
Ohayon MM, 2003, Arch Gen Psychiat, V60, P39
72
Wang SJ
19
Turk DC
236
Kroenke K, 2011, J Pain, V12, P964
61
Wu JW
18
Fishbain DA
228
Blumer D, 1982, J Nerv Ment Dis, V170, P381
46
Ferrari MD
15
Wolfe F
223
Romano JM, 1985, Psychol Bull, V97, P18
46
Hung CI
15
Vonkorff M
202
Arnow BA, 2006, Psychosom Med, V68, P262
44
Liu CY
15
∗∗American Psychiatric Association
199
Karp JF, 2005, J Clin Psychiat, V66, P591
40
Arnold LM
13
Radloff LS
195
Currie SR, 2004, Pain, V107, P54
38
Ayata C
13
Breslau N
182
Demyttenaere K, 2006, J Affect Disorders, V92, P185
37Figure 10
Trends in the percentage of single- vs multiple-authored articles per 5 years.


## 3.7. Analysis of References

Analysis of references was regarded as an important indicator in bibliometric study. The scientific relevance of the published papers was presented in the cocitation map of references (Figure11). The modularity Q score was 0.8897 (higher than 0.5), which indicated that the network was reasonably distributed to loosely coupled clusters. All clusters were traced by index terms extracted from the references. The “rehabilitation outcome” was labeled as the largest cluster #0, followed by “home care” as the second largest cluster #1, “pain comorbidity” as the third largest cluster #2, and “depressive disease.” As shown in Figure 11, the top 23 clusters were showed in a timeline view.Figure 11
The analysis of references. Cocitation map (timeline view) of references from publications on to pain and depression research.


## 3.8. Analysis of Keywords

The keywords of the 2,519 published papers were extracted by CiteSpace V. Figure12 reveals the top 47 keywords with the strongest citation bursts. Keywords with the strongest citation bursts beginning in 1991 were as follows: “disease,” “illness,” “chronic pain,” and “inventory.” The top 47 keywords by the end of 2018 included “older adult” (2014–2018), “validity” (2015–2018), “impact” (2016–2018), and “association” (2016–2018).Figure 12
The keywords with the strongest citation bursts of publications on pain and depression research.


## 3.9. Characteristics of Top 10 Papers Cited Most Frequently

Table3 showed the top ten papers on comorbid pain and depression research with the most citation frequency. The top 10 papers contributed to 7.81% (5,831 citations) of the total number of citations. The article by Bair et al. [31] published in 2003 was the most cited (1,442 citations) paper, and the article is entitled “Depression and pain comorbidity-a literature review.” published in Archives of Internal Medicine. Among the top 10 papers, five [31–35] were published in journals with impact factor≥10 (Archives of Internal Medicine, Brain, Psychological Bulletin and Neuron), two [36, 37] in journals with 5≤impactfactor<10 (Neurology, Arthritis & Rheumatology), two [38, 39] in journals with 3≤impactfactor<5 (Clinical Journal of Pain, Journal of Pain), and one [40] journal with 1≤impactfactor<3 (The Journal of Nervous and Mental Disease).Table 3
The top 10 papers with the most citation frequency in the pain and depression research.
Title
First author
Journal
Impact factor
Year
Citations (WoS)
WoS categories
Category ranking
Depression and pain comorbidity-a literature review
Bair MJ
Archives of Internal Medicine
17.33IF 2014
2003
1442
Medicine, General, & Internal
6/154
Pathophysiology of the migraine aura. The spreading depression theory
Lauritzen M.
Brain
10.848
1994
785
Clinical Neurology; Neurosciences
6/197; 13/261
Chronic pain-associated depression: antecedent or consequence of chronic pain? A review
Fishbain DA
Clinical Journal of Pain
3.209
1997
585
Anesthesiology; Clinical Neurology
11/31; 69/197
Chronic pain and depression: does the evidence support a relationship?
Romano JM
Psychological Bulletin
13.25
1985
513
Psychology; Psychology, Multidisciplinary
3/78; 4/135
Amitriptyline relieves diabetic neuropathy pain in patients with normal or depressed mood
Max MB
Neurology
8.055
1987
462
Clinical Neurology
13/197
Chronic pain as a variant of depressive disease: the pain-prone disorder
Blumer D
The Journal of Nervous and Mental Disease
1.94
1982
460
Clinical Neurology; Psychiatry
134/197; 89/142
Explaining high rates of depression in chronic pain: a diathesis-stress framework
Banks SM
Psychological Bulletin
13.25
1996
434
Psychology; Psychology, Multidisciplinary
3/78; 4/135
A double-blind, multicenter trial comparing duloxetine with placebo in the treatment of fibromyalgia patients with or without major depressive disorder
Arnold LM
Arthritis & Rheumatology
7.379
2004
392
Rheumatology
1/22
Common chronic pain conditions in developed and developing countries: gender and age differences and comorbidity with depression-anxiety disorders
Tsang A
Journal of Pain
4.859
2008
382
Clinical Neurology; Neurosciences
27/197; 51/261
A Cacna1a knockin migraine mouse model with increased susceptibility to cortical spreading depression
van den Maagdenberg AMJM
Neuron
14.319
2004
376
Neurosciences
7/261


## 4. Discussion

### 4.1. Global Trends of the Comorbidity of Pain and Depression Research

The results of our bibliometric study provide a systematic overview on the comorbidity of pain and depression research in the recent forty years. The global trends of published papers showed a statistical continued growth over time in the comorbidity of pain and depression research. Although the percentage of publication increased steadily year by year, a noticeable growth was found between 2001 and 2004 in the year-over-year percentage of publication. Among the eight 5 years, 2014-2018 had the largest number of publications (858) and 2005-2009 had the largest number of citations (17,528) and the highest value ofH-index (66).In accordance with the number of publications on comorbid pain and depression research, the top 20 journals contributed to 29.37% (740 publications) of the total number of publications.Pain contributed to the most publications on comorbid pain and depression research (5.39%) followed by Clinical Journal of Pain (2.26%), Headache (2.26%), and Cephalalgia (1.98%). According to the impact factors of the journals in the Journal Citation Reports (2017 edition), the impact factors were less than 10 among the top 20 journals. In the top 20 journals, the journals with 2≤impactfactor<3 contribute to 40% of the top 20 journals, the journals with 3≤impactfactor<5 contribute to 50%, and the journals with 5≤impactfactor<10 contribute to 10%. However, according to journal IF quartile of Web of Science, 55% of the top 20 journals were Q1 and 40% of the top 20 journals were Q2.In accordance with the number of publications, USA led the first research echelon (1,105), followed by England (178), Canada (156), and Germany (139). And the top 10 countries were from five European countries, three Asia-Pacific countries, and two American countries. As demonstrated in Figure7, it had an extensive collaboration between countries. A total of 1,884 institutions contributed to the publications on comorbid pain and depression research. According to the number of publications, nine institutions were from USA and one from England. Compared with the cooperation of countries, the institutions were not significant.


### 4.2. Research Focuses on the Comorbidity of Pain and Depression Research

According to subject categories of Web of Science, the most popular research areas wereClinical Neurology (725), followed by Neurosciences (577), Psychiatry (560), and Anesthesiology (359). The top 10 subject categories were Clinical Neurology, Neurosciences, Psychiatry, Anesthesiology, Medicine General Internal, Psychology Clinical, Pharmacology Pharmacy, Rheumatology, Psychology, and Rehabilitation. On the basis of types of pain, research topics of the 2,519 papers mainly focused on headache and low back pain for the comorbid pain and depression research. Among the top 10 types of pain (headache, low back pain, animal models of pain, fibromyalgia, neuropathic pain, arthritis, cancer pain, postsurgical pain, visceral pain, and neck pain), headache had the largest number of publications (481), citations (15,674), and open access papers (135) and the highest value of H-index (59). According to the cocitation map of references, the “rehabilitation outcome” was labeled as the largest cluster #0, followed by “home care” as the second largest cluster #1, “pain comorbidity” as the third largest cluster #2, and “depressive disease.” According to the keywords with strongest citation bursts, the results found that the top 47 keywords that began in 1991 were as follows: “disease,” “illness,” “chronic pain,” and “inventory.” And the top 47 keywords by the end of 2018 were as follows: “older adult” (2014-2018), “validity” (2015-2018), “impact” (2016-2018), and “association” (2016-2018). In the last 10 years, because of the aging of the global population, the comorbidity of pain and depression research was rapidly increasing in the older adult. The comorbid pain and depression research gradually transitioned from phenomenon to mechanism. The study by Descalzi et al. [41] showed that their findings not only confirm molecular links on comorbid pain and depression but also provided a potential therapeutic approach.


### 4.3. Strengths and Limitations

This study is the first bibliometric analysis to assess the trends of the comorbid pain and depression research from SCI-Expanded of Web of Science in the recent forty years. Furthermore, to gain rich data, it was not restricted to one academic journal. The 2,519 papers on comorbid pain and depression research were published in 251 different academic journals. Moreover, bibliometric analysis of our study not only covered the number of publications, citations, journals, and collaborations between countries/institutions/authors but also included analysis of keywords, cocitation analysis on references and authors, Web of Science subject categories, and types of pain.This bibliometric study has some limitations. The electronic database is limited to SCI-Expanded of Web of Science, and other electronic databases are not searched and analyzed, for example, PubMed, Embase, Scopus, Cochrane Library. Furthermore, the non-English papers were excluded. Most included papers use English in this study; however, the limitation may induce a publication bias. The last limitation is that influential publications were not cited with high citation frequency, since some potential influential papers were published recently, which could be not cited with frequent times.


## 4.1. Global Trends of the Comorbidity of Pain and Depression Research

The results of our bibliometric study provide a systematic overview on the comorbidity of pain and depression research in the recent forty years. The global trends of published papers showed a statistical continued growth over time in the comorbidity of pain and depression research. Although the percentage of publication increased steadily year by year, a noticeable growth was found between 2001 and 2004 in the year-over-year percentage of publication. Among the eight 5 years, 2014-2018 had the largest number of publications (858) and 2005-2009 had the largest number of citations (17,528) and the highest value ofH-index (66).In accordance with the number of publications on comorbid pain and depression research, the top 20 journals contributed to 29.37% (740 publications) of the total number of publications.Pain contributed to the most publications on comorbid pain and depression research (5.39%) followed by Clinical Journal of Pain (2.26%), Headache (2.26%), and Cephalalgia (1.98%). According to the impact factors of the journals in the Journal Citation Reports (2017 edition), the impact factors were less than 10 among the top 20 journals. In the top 20 journals, the journals with 2≤impactfactor<3 contribute to 40% of the top 20 journals, the journals with 3≤impactfactor<5 contribute to 50%, and the journals with 5≤impactfactor<10 contribute to 10%. However, according to journal IF quartile of Web of Science, 55% of the top 20 journals were Q1 and 40% of the top 20 journals were Q2.In accordance with the number of publications, USA led the first research echelon (1,105), followed by England (178), Canada (156), and Germany (139). And the top 10 countries were from five European countries, three Asia-Pacific countries, and two American countries. As demonstrated in Figure7, it had an extensive collaboration between countries. A total of 1,884 institutions contributed to the publications on comorbid pain and depression research. According to the number of publications, nine institutions were from USA and one from England. Compared with the cooperation of countries, the institutions were not significant.


## 4.2. Research Focuses on the Comorbidity of Pain and Depression Research

According to subject categories of Web of Science, the most popular research areas wereClinical Neurology (725), followed by Neurosciences (577), Psychiatry (560), and Anesthesiology (359). The top 10 subject categories were Clinical Neurology, Neurosciences, Psychiatry, Anesthesiology, Medicine General Internal, Psychology Clinical, Pharmacology Pharmacy, Rheumatology, Psychology, and Rehabilitation. On the basis of types of pain, research topics of the 2,519 papers mainly focused on headache and low back pain for the comorbid pain and depression research. Among the top 10 types of pain (headache, low back pain, animal models of pain, fibromyalgia, neuropathic pain, arthritis, cancer pain, postsurgical pain, visceral pain, and neck pain), headache had the largest number of publications (481), citations (15,674), and open access papers (135) and the highest value of H-index (59). According to the cocitation map of references, the “rehabilitation outcome” was labeled as the largest cluster #0, followed by “home care” as the second largest cluster #1, “pain comorbidity” as the third largest cluster #2, and “depressive disease.” According to the keywords with strongest citation bursts, the results found that the top 47 keywords that began in 1991 were as follows: “disease,” “illness,” “chronic pain,” and “inventory.” And the top 47 keywords by the end of 2018 were as follows: “older adult” (2014-2018), “validity” (2015-2018), “impact” (2016-2018), and “association” (2016-2018). In the last 10 years, because of the aging of the global population, the comorbidity of pain and depression research was rapidly increasing in the older adult. The comorbid pain and depression research gradually transitioned from phenomenon to mechanism. The study by Descalzi et al. [41] showed that their findings not only confirm molecular links on comorbid pain and depression but also provided a potential therapeutic approach.


## 4.3. Strengths and Limitations

This study is the first bibliometric analysis to assess the trends of the comorbid pain and depression research from SCI-Expanded of Web of Science in the recent forty years. Furthermore, to gain rich data, it was not restricted to one academic journal. The 2,519 papers on comorbid pain and depression research were published in 251 different academic journals. Moreover, bibliometric analysis of our study not only covered the number of publications, citations, journals, and collaborations between countries/institutions/authors but also included analysis of keywords, cocitation analysis on references and authors, Web of Science subject categories, and types of pain.This bibliometric study has some limitations. The electronic database is limited to SCI-Expanded of Web of Science, and other electronic databases are not searched and analyzed, for example, PubMed, Embase, Scopus, Cochrane Library. Furthermore, the non-English papers were excluded. Most included papers use English in this study; however, the limitation may induce a publication bias. The last limitation is that influential publications were not cited with high citation frequency, since some potential influential papers were published recently, which could be not cited with frequent times.


## 5. Conclusions

This study provides historical insights into the trends of comorbidity of pain and depression research. The number of published papers significantly increased over the last 40 years, and the overall trend of publications increased from 5 publications in 1980 to 179 publications in 2018. Although this study presents several limitations, it adequately exposes the trends of comorbidity of pain and depression research. Based on the type of pain, the research topics of the 2,519 papers included in this work mainly focused on headache, low back pain, and fibromyalgia. The results of our study could provide useful information for pain and depression researchers, funding agencies, and policy makers.



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*Source: 1657498-2019-10-23.xml*