The international platform of registered systematic review and meta-analysis protocols (INPLASY) at 3 years: an analysis of 4,658 registered protocols on inplasy.com, platform features, and website statistics

Background INPLASY® is an international platform for registering systematic reviews and meta-analysis protocols that was launched in March 2020. INPLASY® provides an online database in which the protocols are maintained as permanent public records and can be accessed on its website (www.inplasy.com). Methods We described the database features and registered information of all records published since the launch of the registry on March 31, 2023. Additionally, we analyzed the website statistics dataset to explore user experience and promote data transparency. Results Four thousand six hundred fifty-eight records were registered in INPLASY®, and more than 94% of the protocols were published within 24 h. Most of the submissions were from China, followed by Portugal, Taiwan, Malaysia, and Brazil. The INPLASY® website received 386,395 page views from 64,568 visitors during the first three years. The accesses were obtained from 170 countries. Most of the accesses were from China, followed by the US, the UK, and Portugal. The review status “completed and published” was observed in 898 protocols, and these studies were published in 372 different scientific peer-reviewed journals. The features of INPLASY® include the following: (i) INPLASY® identifier, a unique protocol number; (ii) the digital object identifier (DOI) number, the URL of the protocol linked to a specific DOI; (iii) ORCID update, INPLASY® automatically updates authors' ORCID page, including their protocol; and (iv) search tools, the protocols are freely accessible on www.inplasy.com. Conclusions INPLASY® has several practical and useful features that should be considered when planning the registration of a systematic review protocol. Furthermore, the sharp increase in the number of protocols registered in INPLASY® in the first three years and the database statistics demonstrate that INPLASY® has become an important source of systematic review protocols. Therefore, authors should access INPLASY® before planning a future review study to avoid unintended duplication of efforts and to obtain timely registration.


. Background
The registration of systematic review protocols is crucial to avoid duplication of systematic reviews and improve transparency (Straus and Moher, 2010;Dos Santos et al., 2020). The protocol specifies the objectives and methods that will be applied to conduct the review, enabling authors to track what studies are taking place (Chang and Slutsky, 2012). Additionally, discrepancies between the methods described in the protocol and those in the published review can be identified, allowing readers to analyze outcome reporting biases associated with the study. PROSPERO (Booth et al., 2011) was the first prospective registry for systematic review protocols; however, recently, alternative platforms have become available (Pieper and Rombey, 2022).
INPLASY R is an international publicly accessible platform for registering systematic reviews and meta-analysis protocols, which was officially launched in March 2020 The INPLASY R registry provides an online platform to register systematic review protocols, which are maintained as permanent public records and are free of access on inplasy.com. Although PROSPERO was the first available registry, it seems challenging for a single platform to register all systematic review protocols developed worldwide. Additionally, PROSPERO was supported by the National Institute for Health Research (NIHR), and submissions from the UK were prioritized during the registration process. In contrast, INPLASY R does not prioritize protocols based on the nationality of authors, providing the same registration time for all submissions. Furthermore, INPLASY provides other relevant features, such as a digital object identifier (DOI) number to easily cite each protocol and an automatic update system connecting the protocol with the final published article. An important difference between PROSPERO and INPLASY is that PROSPERO does not accept systematic reviews without an outcome of clear relevance to human health. Conversely, INPLASY does not impose any such restrictions, and other review projects, such as scoping reviews, are accepted for registration.
We aim to describe the important features of the new international database and summarize the information from all records published in the database since the launch of the INPLASY R registry. Additionally, we collated a website statistics dataset to explore user experience and promote platform transparency.
PROSPERO International prospective registry of systematic reviews.
INPLASY International platform of registered systematic review and metaanalysis protocols. Available online at: www.inplasy.com.

. Methods
We collected the following data from all protocols published on inplasy.com from its inception until March 31, 2023: (i) the type of review protocol described in the title, such as systematic review, scoping review, overview of reviews, meta-synthesis, mapping review, rapid review, meta-analysis, or network metaanalysis; (ii) study phase at which the protocol was registered (prospective or retrospective registration); (iii) the country of the corresponding author; and (iv) the number of versions of each protocol.
The . Results  Most submissions were from China, followed by Portugal, Taiwan, Malaysia, and Brazil. There were 5,782 subscribers in March 2023. The number of registered users per month is shown in Figure 2. The registered protocols were from 63 countries where they were developed. Of these, 86.6% were from Asia, 8.0% from Europe, 4.0% from America, 0.62% from Africa, and 0.60% from Australia/Oceania. The types of reviews registered are presented in Table 1. Approximately 80% of registered protocols were obtained from systematic reviews and/or metaanalyses.

. . Database statistics
The INPLASY R website received 386,395 page views from 64,568 visitors during the first 3 years. The accesses were from 170 different countries, most of which were from China, followed by the US, the UK, and Portugal.

. . Registration time and review status
Three thousand nine hundred fifty-seven protocols were registered prospectively (84.9%), and 701 protocols (15.1%) were registered retrospectively. The review status "completed and published" was observed in 898 protocols, published in 372 different scientific journals. Figure 3 shows the annual publication rate. Only 0.1% of the INPLASY R protocols presented the updated review status as "discontinued" by authors. Additionally, 692 records registered in INPLASY R were published as stand-alone peer-reviewed protocols (14.85% of the sample), which were published in twelve scientific journals ( protocol, which can be used to identify the review protocol in the final manuscript. Additionally, all protocols registered on inplasy.com have a DOI, and the URL in which each protocol is hosted is permanently linked to a specific DOI. including systematic reviews of interventions, diagnostic accuracy, prognostic factors, epidemiological characteristics, and preclinical studies. Systematic reviews assessing sports performance as outcomes are also accepted. Authors can submit scoping review protocols using a standard systematic review form or a specific form developed exclusively for scoping reviews (https://inplasy.com/ scoping-reviews/), using the JBI manual for evidence synthesis (Shamseer et al., 2015). One hundred and seventeen scoping review protocols were published in INPLASY R (2.52% of the sample).

. . . Processing time
Four thousand six hundred fifty-eight published protocols were analyzed to determine the period between protocol submission and publication. Ninety percent of the records were published within 24 h, whereas <1% of the records took over 48 h to be published because of technical issues in the platform or failure during the submission process.

. . . Version tracking-updating a published protocol
Authors can update their protocols using the INPLASY R update form. We identified 4,333 protocols with a single version, 288 protocols with two versions, 29 protocols with three versions, and eight protocols with four versions. All previous versions of the protocol were permanently maintained on the protocol page updates the author's ORCID page using the Crossref interface. Alternatively, authors can manually update their ORCID pages using the DOI number of the protocol. This feature was used in 589 (12.64%) protocols in which at least one of the authors of the registered protocol included ORCID details.
. . . Funding model INPLASY R was created by a for-profit organization to provide an online public platform on which researchers could register systematic review protocols. The publication fees as of June 2023 were $20 to register a protocol and $9 to update it. During the first 3 years, INPLASY R did not receive funding from government agencies, universities, or other institutions. Therefore, publication fees were the only source of financing during this period. Although a for-profit organization operates the platform, there is an ongoing process involving the public ministry of Distrito Federal Brazil to create a non-profit company for controlling the INPLASY registry. With this transformation, a significant change in the origin of resources for the platform's maintenance is expected by 2023, eliminating any potential conflicts of interest in the forprofit model.

. . . Search structure
The INPLASY R platform offers a simple search tool where records can be found according to the unique identifier number or using free text terms. By June 2023, the Boolean operators (AND, OR, and NOT) could not be used on a search page.

. . . Review process
The INPLASY platform conducts a basic review to certify that a protocol is eligible for registration on the platform. The INPLASY records are not peer-reviewed or assessed for methodological quality. This is the responsibility of authors. The methods or content registered on INPLASY do not constitute an endorsement of methods that are solely those of authors. Additionally, INPLASY does not guarantee the accuracy of the English and is not responsible for errors arising from the text.

. Discussion
Since the launch of INPLASY R in March 2020, the number of records has increased progressively, reaching 4,658 protocols in 63 countries by March 31, 2023. After 3 years of operation, INPLASY R has become the second-largest specific database for the registration of systematic reviews, behind PROSPERO in terms of the number of protocols (Pieper and Rombey, 2022). The INPLASY R protocol was developed based on PRISMA-P recommendations (Shamseer et al., 2015)  waste because the longer the time interval between the submission and the registration, the greater the chances of duplicated protocols. As the platform does not follow a peer-reviewed process, quick registration is possible. Solla et al. (2020) showed that PROSPERO registration does not prevent two registrations on the same topic. Therefore, authors are responsible for searching for ongoing systematic reviews in the pipeline before submitting their review protocols. COVID-END, a time-limited network group formed by over 50 of the world's leading evidence-synthesis, indicated that before starting a new project, researchers should seek ongoing reviews not only in PROSPERO but also in the INPLASY R platform, the National Collaborating Center, the Center for Evidence-based Medicine, and the VA Evidence Synthesis Program Other available platforms for the registration of systematic review protocols include Cochrane Reviews, Joanna Briggs Institute, and Campbell Collaboration, which provide quality assurance and many other benefits for accepted review protocols. However, these platforms are highly restricted, and only a small number of selected protocols can be published.
Additionally, these organizations produce only a minority of all systematic reviews (Page et al., 2016). Banno et al. (2022) identified the frequency of systematic review protocols being registered outside the PROSPERO registry until 2019. They listed generic registries that accepted systematic review protocols. Pieper and Rombey (2022)  High-quality protocols can be obtained by submitting records to peer-reviewed journals after registration. Several journals, such as PLoS ONE, BMJ Open, and Systematic Reviews, have published systematic review protocols as stand-alone peer-reviewed articles. The advantage is that the methods proposed in the protocol are critically appraised, thereby increasing the quality of the report and preventing potential flaws that may compromise the validity of the study. However, most systematic reviews do not refer to peer-reviewed protocols. Only 14.85% of all protocols registered in INPLASY R were published in peer-reviewed journals, confirming that most systematic review protocols have not yet been peer-reviewed.

. Conclusion
Overall, the present findings indicate that the INPLASY platform has many desirable features and should be considered a reliable and fast platform for registering systematic review protocols.

Additionally, INPLASY
R provides an option to register other evidence synthesis protocols, such as scoping, methodological, and rapid reviews. The sharp increase in the number of protocols registered in INPLASY R in the first 3 years and the database statistics demonstrate that it has become an important source of systematic review protocols. Therefore, authors should access INPLASY R before planning a future review study to avoid unintended duplication of efforts and to obtain timely registration.

Data availability statement
Publicly available datasets were analyzed in this study. This data can be found at: inplasy.com/projects.

Author contributions
JC: conceptualization, data curation, formal analysis, investigation, writing-original draft preparation, supervision, and finally reviewed the manuscript. FR: data curation, formal analysis, validation, visualization, and writing-original draft preparation. AR and EA: visualization and writing-review and editing the manuscript. GF: data curation, investigation, validation, and writing-review and editing the manuscript. CF: data curation, validation, and writing-review and editing the manuscript. MV: formal analysis, supervision, and writing-review and editing the manuscript. All authors contributed to the article and approved the submitted version.