Background: The purpose of this study was to identify the top 100 cited articles dedicated to sleep medicine published in journals that have made key contributions to the field. Methods: We performed a search of journals and selected 100 top-cited articles by utilizing the Institute for Scientific Information database available under the banner of the Web of Science. Next, we manually reviewed the contents of the top 100 cited articles. We examined the characteristics of the articles, such as the number of citations, ranking, authorship, article title, year of publication, publishing journal, publication type, and topic categories. Results: The top-cited articles were published in 49 journals, and the most frequently cited journal was Sleep (23 articles). The top 100 cited articles originated from institutions in 9 countries, with the USA contributing 67 articles. The institution associated with the largest numbers of sleep medicine citation classics was Stanford University (11 articles). Morin CM, who was the first author for 6 articles, was listed most frequently in the sleep medicine citation classics. The publication years were concentrated in the 2000s, when 42 articles were published. The topics included 35 insomnia studies, 25 sleep physiology studies, 22 obstructive sleep apnea studies, and 19 other studies. Conclusions: The present study provides a detailed list of the most-cited articles on sleep medicine. This currently relevant approach provides an opportunity to recognize the classic articles on sleep, to provide useful insights into international leaders, and to describe research trends in the field of sleep medicine.

Sleep is necessary, but its function, physiology, and pathophysiology have only been unfolding in this century. However, in the past 50 years, significant advances have been made in the scientific understanding of sleep and its disorders, which has galvanized the establishment of sleep as an important clinical discipline [1]. Recognition of the importance of sleep and its disorders is increasing among the medical profession and the public. More than 80 different types of sleep disorders have been currently defined [1]. Sleep disorders are very common, with the prevalence of adjustment insomnia being approximately 15–20% and that of obstructive sleep apnea in adults being 4–24% in men and 2–9% in woman depending on studies [1-3].

The number of citations of previously published work is an indicator of its subsequent recognition and impact in an area of study [4-6]. The number of citations is a proxy to an article’s quality, and reviewing articles that are frequently cited can provide information about the dominant areas of a discipline, as well as highlight the growth of particular fields. Furthermore, top-cited articles are often written by recognized experts who can offer insights into the future directions of the discipline. The study and analysis of citation indexes have resulted in the development of various metrics to assess the impact of scientific journals or individual investigators based on the number of citations to their respective works [4-6].

Several recent studies have identified and analyzed citation classics and top-cited articles in various medical fields, including general surgery [7], anesthesiology [8], emergency medicine [9], plastic surgery [10], dermatology [11], obstetrics and gynecology [12], orthopedic surgery [13], critical care medicine [14], and headache disorders [15]. However, to the best of our knowledge, no comprehensive study of the top-cited articles in the field of sleep medicine has been made available to date. The purpose of this study was to identify the 100 most-cited articles published in journals dedicated to sleep medicine that have made key contributions to the field. Identifying a reliable and unified set of core journals in the field of sleep medicine may be of interest to investigators within this field.

We performed a citation analysis in the field of sleep medicine. Citation analysis is a bibliometric method that examines the frequency and patterns of citations in articles, under the banner of the Web of Science (https://www.webofknowledge.com), providing the most relevant bibliometric information from published scientific articles by Clarivate Analytics.

First, in January 2020, we performed a search of articles published since 1970 with title words including “sleep,” “insomnia,” “parasomnia,” “hypersomnia,” “polysomnography,” or “sleepiness.” Second, we selected the most-cited 100 articles. Third, we manually reviewed the contents of these articles, examining characteristics such as the number of citations, ranking, authorship, article title, year of publication, publishing journal, publication type, and topic categories. The publication types were categorized into original articles, case series, and systemic review/guidelines, and the topic types were subtyped as obstructive sleep apnea, insomnia, hypersomnia, parasomnia, sleep physiology, questionnaire, polysomnography, and guidelines. When the authors of an article had more than one affiliation, the department, institution, and country of origin were defined by the affiliation of the first author. Data are presented using descriptive statistics, and no tests of statistical significance were performed. This study did not need to be reviewed by an ethics committee because it is a bibliometric analysis of existing published studies and did not involve human subjects.

We selected the 100 most frequently cited articles for analysis and ranked them according to the number of citations (Table 1). The most-cited article received 10,154 citations, and the least cited article received 150 citations. The majority of articles (75 articles) received more than 300 citations.

Table 1.

Top 100 cited articles in the field of sleep medicine

Top 100 cited articles in the field of sleep medicine
Top 100 cited articles in the field of sleep medicine

The top-cited articles were published in 49 journals (Table 2). Of the 49 journals, the most frequently cited journal was Sleep (25 articles), followed by Lancet (6 articles), Archives of General Psychiatry (5 articles), and JAMA Neurology, Nature, and Science (4 articles).

Table 2.

Journals with two or more of the top 100 cited articles in the field of sleep medicine

Journals with two or more of the top 100 cited articles in the field of sleep medicine
Journals with two or more of the top 100 cited articles in the field of sleep medicine

The top 100 cited articles originated from institutions in 9 countries, with the USA contributing 66 articles, followed by Canada (10 articles), the UK (7 articles), and Germany (5 articles) (Table 3). Seventy-six of the articles originated from the North American continent, including the USA and Canada; 30 articles originated from countries in Europe, including the UK, Germany, Italy, Switzerland, Spain, and France; and only 4 articles originated from countries in Asia and Oceania, including Australia.

Table 3.

Country of origin of the top 100 cited articles in the field of sleep medicine

Country of origin of the top 100 cited articles in the field of sleep medicine
Country of origin of the top 100 cited articles in the field of sleep medicine

Tables 4 and 5 list the top-ranked institutions and authors for the published sleep medicine citation classics. The 10 institutions provided 5 or more top-cited articles. The institution associated with the largest number of sleep citation classics was Stanford University in the USA (11 articles), followed by Harvard University and Wisconsin University in the USA (9 articles) and Laval University in Canada (7 articles). Morin CM, who was the first author for 6 articles, was listed most frequently in the sleep medicine citation classics.

Table 4.

Institution of origin of the first authors with 5 or more top 100 cited articles in the field of sleep medicine

Institution of origin of the first authors with 5 or more top 100 cited articles in the field of sleep medicine
Institution of origin of the first authors with 5 or more top 100 cited articles in the field of sleep medicine
Table 5.

First authors with two or more of the top 100 cited articles in the field of sleep medicine

First authors with two or more of the top 100 cited articles in the field of sleep medicine
First authors with two or more of the top 100 cited articles in the field of sleep medicine

The decade of publication with the most relevant articles identified is listed in Figure 1. The publication years were concentrated in the 2000s, when 42 of the citation classics were published. Furthermore, 25 of the 100 top-cited articles were published in the 1990s. The earliest recorded article was published in 1972, and the most recent article was in 2013. With regard to the types of articles, 75 were original articles/guidelines and 25 were systemic review articles. The topics included 33 insomnia studies, 26 sleep physiology studies, 22 obstructive sleep apnea studies, 7 questionnaire studies, 4 hypersomnia studies, 3 polysomnography studies, 3 guidelines, and 2 parasomnia studies.

Fig. 1.

The decade of publication with topics. The figure shows that the publication years are concentrated in the 2000s. The topics of most articles are regarding insomnia, sleep physiology, or obstructive sleep apnea.

Fig. 1.

The decade of publication with topics. The figure shows that the publication years are concentrated in the 2000s. The topics of most articles are regarding insomnia, sleep physiology, or obstructive sleep apnea.

Close modal

In this study, we identified and characterized the top 100 cited articles in the field of sleep medicine. These citation classics may enable the identification of a seminal advance in sleep medicine and provide a historical perspective on scientific progress in the field of sleep medicine.

The top-ranked article was titled “The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research” authored by Buysse DJ in 1989 [16]. It was cited 10,154 times. The Pittsburgh Sleep Quality Index is a questionnaire that evaluates sleep quality during the previous month. It consists of 18 questions about subjective sleep quality, sleep latency, sleep duration, sleep efficiency, use of medications in sleep, daytime sleepiness, and factors that affect sleep quality. It was not designed specifically for insomnia but has also been used in the assessment of insomnia and treatment studies. As a questionnaire is a research instrument for another study and might be useful to compare findings across studies, it could be frequently cited in many articles.

Citation analysis is based on the premise that top-cited articles are likely to be championed by recognized experts to demonstrate emerging topics within their particular field and to offer a useful indication of relevant trends in that field [4, 5]. In the present study, we took advantage of these tools to identify important works in the field of sleep medicine. The topics of the classic articles varied from decade to decade, and we discovered some interesting trends in the topics over time. We noted that the most-cited articles concerning sleep medicine were published around the 2000s. It is remarkable that the majority of these relatively recent articles were cited and have an influence in the field of sleep medicine. This result is not consistent with other studies that used bibliometric analysis, which usually demonstrates that the most-cited articles were published around the 1990s. Thus, we could infer that sleep medicine has undergone much development in more recent years, and this trend may be attributed to recent large developments in the research techniques of this field.

We also demonstrated that the most-cited articles were published in the journal Sleep, which is the official publication of the Sleep Research Society. This is perhaps related to the fact that the high impact factors among sleep-specific journals belong to sleep medicine. Moreover, we found that about half of the 100 top-cited articles originated from institutions in the USA, which is consistent with the overwhelming influence of the USA in health science research reported by other top-cited articles in different clinical disciplines [7-10]. Institutions in the USA have greatly contributed to the development of research in the field of sleep medicine. This could be explained by the large size of the US scientific community and their higher research budget. Moreover, it was reported that the authors in the USA usually prefer to publish in journals from the USA and preferentially cite local articles [17]. However, interestingly, the institution associated with the other largest number of sleep medicine citation classics was Laval University, which is the oldest French-language university in North America, located in Quebec City of Canada (not in the USA). We also found that only 4 articles of the 100 top-cited articles originated from Asian and Oceanian countries, including Australia, despite a recently increasing number of articles originating from Asian countries in the field of neurology research [18].

The most popular topic in the most-cited articles was insomnia. This might have originated from increased concerns regarding quality of life and insomnia. In addition, insomnia is the one of the most common medical complaints that generates over 5 million office visits per year in the USA alone [19]. It also frequently coexists with other medical, psychiatric, sleep, or neurological disorders. We can assume that research regarding insomnia might increase with time.

There were inherent limitations in the current citation classics. There is obviously considerable debate regarding the value of citation rates. The argument is that the greater the value of the article, the more times it will be cited [20]. The number of citations top articles accrue depends on factors other than quality and originality. Although the work with a highly cited article has an impact on the scientific community, other factors, such as researchers, institutions, and funding agencies, can gauge their productivity and impact quantitatively [21]. In addition, citations do not distinguish between positive and negative references [20]. Moreover, the method of the use of total citations favors older publications and older journals [22]. The citation of a scientific article usually follows a time lapse and is usually not cited until 1–2 years after publication, reaches a peak after 3–10 years, and then declines [23]. This normal life span of a publication shows that evaluating the rank and significance of recent publications is limited. In addition, the citation count profiles of articles published in medical journals are sometimes different according to the citation databases, such as the Web of Science, Scopus, or Google Scholar. Google Scholar and Scopus usually retrieve more citations per article than the Web of Science [24]. Furthermore, certain types of articles, including systematic reviews, meta-analyses, or guidelines, usually have a higher citation rate than other study designs [25]. However, the use of citation rates is widely accepted as the best method of judging the merits of specific journals. The impact factor is widely indicative of the importance of a given journal in its specific field of interest and has emerged as a marker of the quality and rank of the journal [26]. Thus, although citation statistics have been frequently criticized, the analysis of citation rates can allow for the identification of advances in a specialty and may provide a historical perspective of its scientific progress.

The present study provides a detailed list of the most-cited articles on sleep medicine. This currently relevant approach provides an opportunity to recognize the classic articles on sleep medicine, provide useful insights into international leaders, and describe research trends in the field of sleep medicine.

All the authors agree with the contents of this manuscript and the statement of ethical issues.

The authors have no conflicts of interest to disclose.

The authors did not receive any funding.

Bong Soo Park drafted the manuscript, Il Hwan Kim interpreted the data, and Kang Min Park designed or conceptualized the study.

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Bong Soo Park and Il Hwan Kim equally contributed to this work.

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