Table 4.

Main themes identified from authors’ explanations of retrospective reporting and example statements

Theme	Example(s)
Unawareness of registration policy	At the time when the trial was started, the initiators of this study were unfortunately unaware of the policy of the International Committee of Medical Journal Editors (ICMJE), which requires prospective registration of all interventional clinical trials. As soon as we became aware of this policy, we registered the trial. (doi: 10.1371/journal.pone.0146678) The reason for retrospectively registering the study was that the study authors were not aware of the recommendation to register diagnostic accuracy studies before this date. (doi: 10.1371/journal.pone.0199345)
Delays by the registry	Registration of the study was applied for in April 2015. All queries from the DRKS were answered until the 31st August 2015 except the planned inclusion date of the first patient (first-patient-in), which was correct in the DRKS registry on 1st December 2015. Confirmation of registration occurred on 4th December 2015. The first patient was recruited and randomized into the study on 20th October 2015. Until 4th December 2015 eight patients were randomized into the trial. (doi: 10.1371/journal.pone.0229898)
Not obligatory at the time	At the time of submission of the study protocol, the Ethics Committee did not require registration for feasibility or proof of concept studies. The study was registered in ClinicalTrials.gov (NCT02196545) in July 2014 in preparation of a manuscript for publication of the data. The authors confirm that all ongoing and related trials for this intervention are registered. (doi: 10.1371/journal.pone.0121478) It was not registered at a clinical trial register, because at the time of setup in 2003, such a registration was not obligatory. (doi: 10.2174/1874325001307010133)
Not obligatory for the intervention	According to national laws it is stipulated to inform the respective ethics committee, but it was not necessary to register the study in an official registry or to obtain an ethics committee vote, because it was an expanded access study (Heilversuch). Despite this, we prospectively obtained a vote of the ethics committee. Study design and patient information form were approved by the local ethics committee (ethics committee of the regional medical association; approval no. EK-BR-50/10–1, date of approval December 10th, 2010). In addition, the study was registered at www.clinicaltrials.gov (ID no. NCT02168790). (doi: 10.1371/journal.pone.0125035)
Miscommunication between investigators	The time of first registration was June 17, 2013, and final approved trial registration was July 1, 2013. First patient inclusion was in July 2012 at the Heart Center Leipzig University Hospital, Leipzig, Germany. Thus, there was a delay between first patient inclusion and trial registration that was the result of a misunderstanding between the principal investigator of the trial, Dr Thiele, and the first author, Dr Fuernau, who was responsible for clinical project coordination at the investigator’s site at the Heart Center Leipzig University of Leipzig. According to initial communication, registration had to be performed by Dr Fuernau. When the study principal investigator recognized that it had not been performed, we immediately registered the trial at http://www.ClinicalTrials.gov. At this time, only 7 patients at the Heart Center Leipzig University Hospital had been included in the trial. (doi: 10.1161/CIRCULATIONAHA.117.032722) (…)there was a delay of trial registration before first patient inclusion which was induced by a misunderstanding between the project coordination for the EU grant (at this time gabo:mi, later on ARTTIC) and the clinical project coordination at the investigator’s site at the Heart Center Leipzig - University of Leipzig. According to initial communication registration should be performed by gabo:mi. When the study coordinator recognized that it has not been performed we immediately registered it at clinicaltrials.gov. At this time only 13 patients at the Heart Center Leipzig University Hospital (and no other study site) have been included into the trial. (doi: 10.1056/NEJMoa1710261)
Publication	Registration was done after the study has been conducted and the results suggested a publication and further continuation of this research. (doi: 10.1186/s12903-016-0264-2)
Confidentiality	The principal investigator (N.H.) delayed the registration of the study until data acquisition was completed for confidentiality reasons concerning the study methods, especially the magnetic resonance with the related morphometric measurements. (doi: 10.1371/journal.pone.0136375)
Logistic/administrative issues	Because of administrative problems, release of registration occurred about six months after study start. The authors confirm that all ongoing and related trials for this intervention are registered. (doi: 10.1371/journal.pone.0220436) Due to organisational changes in the research project shortly before the start of the recruitment we put great efforts into avoiding a delayed start of the data collection in the cooperating inpatient units, which resulted in retrospective study registration and a delayed publication of our study protocol. (doi: 10.1371/journal.pone.0186967) Registration of the trial was delayed after the enrollment of the first patient due to an administrative error. The authors confirm that all ongoing and related trials for this intervention are registered. (doi: 10.1371/journal.pone.0140584)