Therefore, it is vital that the project team includes a statistician with experience of relevant analytic techniques, preferably someone who been part of an IPD meta‐analysis project previously, or familiar with appropriate modelling of large data from clustered sources such as healthcare practices or hospitals. They should also be familiar with the importance of building relationships with trial investigators and how this relates to data assembly, and recognise that analysis is not a stand‐alone activity. For this reason, ‘drafting in’ a statistician to focus only on the analysis is not advised; the statistician must be part of the central team, even if during some periods their involvement is less than at others. It can work well to have a highly experienced statistician, with an established track record in IPD meta‐analysis, to specify appropriate methods and oversee and guide the day‐to‐day work of a more hands‐on but potentially less experienced statistician.
3.6 Advisory and Governance Functions
It is usually helpful to establish an advisory group during the planning stage, as having a strong advisory group that endorses the IPD meta‐analysis project may add to credibility, be helpful in persuading trial investigators to participate, and strengthen funding applications.
As well as providing independent advice, an advisory group can play an important role in garnering wider clinical or topic expertise, and providing additional methodological oversight. It is also a good way to engage patients and the public in a meaningful way, ensuring that the patient voice is heard. Therefore, an advisory group will often include members from different specialties and professions that are relevant to the review topic, representation from patient support groups, individual patients and carers (who will often have a different perspective to support groups), and methodologists. For example, the advisory group for an IPD meta‐analysis project (and linked economic evaluation) examining intensive behavioural interventions based on applied behaviour analysis (ABA) for young children with autism included: representation from the National Autistic Society, research study investigators, parents of children with autistic spectrum disorder, adults with autism spectrum disorder, ABA practice specialists, psychiatrists, clinical and educational psychologists, specialists in IPD meta‐analysis, and health economists.78 Having well‐respected international members of the advisory group might be particularly helpful when requesting IPD from trial investigators working in different countries to the central research team.
As participant‐level data are being used, commissioners may sometimes suggest that an IPD meta‐analysis project should establish governance structures similar to those for a clinical trial. However, with the exception of those that are prospective (Section 3.12), IPD meta‐analysis projects use participant‐level data that have already been collected in existing trials and no new participants are being recruited; therefore, there should usually be no requirement for a steering or data monitoring and ethics committee (as would be needed for a clinical trial).
3.7 Estimating How Long the Project Will Take
Unlike a conventional systematic review, the pace and progress in an IPD meta‐analysis project is not entirely under the control of the research team. The time required for some activities can be reasonably estimated, such as producing a protocol, running searches, eligibility screening, and preparation of a data dictionary (Section 4.2). However, the time taken to assemble, code and check the quality and applicability of received IPD is highly dependent on the actions of the data providers (Sections 4.4 to 4.6), and so is often difficult to estimate in advance.
There is inevitably a lag between inviting trial investigators to participate and receiving IPD. After having been persuaded personally of the value of the proposed project (which may itself take some time), some trial investigators will need to obtain institutional or other approval to release data. This can take several months, particularly if granted at institutional review board or committee meetings, which may be scheduled infrequently. Data and documentation may then have to be located in stores and archives, and prepared for release.
After data have been received, the central research team then need to check the trial IPD and send queries to trial investigators and resolve them. Again, this can take considerable time, particularly if the lead trial investigator needs to liaise with others such as the trial data manager or statistician, to determine exactly how data have been coded or which variables were used to define outcomes in the original trial analyses. It is important to remember that whilst the IPD meta‐analysis may be a top priority for the research team leading it, the same may not be true for trial investigators, who are likely to have many competing demands for their time.
Another important consideration when estimating timing and resource requirements is whether those responsible for included trials would prefer to prepare and code their IPD in the format required for the IPD meta‐analysis project, or whether they prefer to send it in its original format and for the central research team then to do any recoding required. Even when trial investigators prepare data, the central research team still need to spend some time assimilating it. An estimated minimum of around a day should be allowed for processing the data for each trial, and longer if the suggested coding has not been followed as intended. Dealing with data that have not been prepared by the trial investigators can be very time consuming, depending on the complexity of the data and the way that it is structured. For a very large and complex trial dataset, with variables stored across many electronic forms and with, for example, repeated follow‐up and measurements, it may take a team member several weeks to fully understand it, write code to extract and transform data to meta‐analysis format, and to check thoroughly that this has generated the correct values. It can be difficult to estimate what proportion of trials this will apply to. Our experience is that most trial investigators are willing to prepare and recode data, but that it would be wise to factor in time for the research team to prepare data from at least 20% of trials.
Unless there are very specific assurances that IPD will be released rapidly and that any issues encountered during data checking will be resolved promptly by trial investigators, as a rule of thumb, upwards of a year should be planned for collecting and checking the IPD from the full set of eligible trials. IPD collection, cleaning and harmonisation for large projects involving many trials may take much longer than a year, and typically 18 to 24 months is needed prior to the IPD meta‐analysis itself. Much of the elapsed time is taken up by communications and by trial investigators gaining approvals. As older trials may be difficult and time‐consuming to trace, and agreement more difficult to reach for controversial topics, these sorts of issues should also be factored into planning project timelines.
Likewise, there will usually be a lag between requesting IPD from a data repository and subsequent provision of that IPD. There will usually be a process for approving project proposals prior to the release of a trial’s IPD that may take several months to complete. As noted earlier, experience to date has been mixed; whilst some teams have found that communication with the data providers has become more streamlined and that pre‐coded datasets can reduce the time taken to prepare data for analysis,74 others have found that obtaining permissions when multiple data owners are involved has been difficult.75 Based on the limited experience so far, it is sensible to still factor in at least a year to obtain the necessary approvals and gain access to IPD from data repositories and data‐sharing platforms.
As trial data usually arrive sporadically over a period of time, data checking is usually done concurrently with data collection and coding. Data are checked as soon as possible after receipt, and any issues discussed and resolved with trial investigators, usually with a series of iterations (Section 4.5.4). This often includes analysing each trial individually and comparing with any published analyses, both to understand any