What participant information sheets get wrong about retention

A participant information leaflet and a trial protocol are meant to describe the same study. An analysis of 92 adult PILs and 90 corresponding protocols from UK Clinical Trial Units found that, at least when it comes to retention strategies, they frequently don't.

The mismatch is common, not occasional

Among the studies where both the leaflet and the protocol actually discussed retention strategies (59 leaflets with 58 matching protocols), only 18.6% communicated identical information across both documents. Nearly half, 45.8%, only partially matched. More than a third, 35.6%, communicated genuinely different information between what a participant was told and what the protocol actually specified.

That's not a rounding error in how two documents happen to phrase the same plan differently. In over a third of cases, a participant reading the information sheet would have formed a different understanding of how the study intended to keep them engaged than what the protocol, the actual governing document, described. Given that 81.5% of the leaflets examined did include some form of retention plan at all, most trial teams are clearly trying to communicate this. The problem sits in whether that communication tracks the plan that's actually operating.

What retention strategies actually got mentioned

Where leaflets did describe a retention approach, 57% described a combination of strategies rather than a single tactic, and the most commonly named individual approach, appearing in 16% of leaflets, was scheduling data collection around routine care visits participants were already attending anyway. That's a sensible, low-burden strategy on its face. Whether it survived intact into the version participants actually experienced is exactly the question the mismatch data leaves open.

A separate, smaller gap is worth noting alongside the bigger one: fewer than 7% of leaflets explained why retention actually matters, specifically, that missing or withdrawn data affects the study's ability to answer its research question at all. Only 6.5% addressed the importance of retention generally, and just 5.4% connected that to the concrete impact of missing or deleted data on the results. Most participants asked to stay engaged in a study are, on this evidence, rarely told what's actually at stake if they don't.

Why this matters beyond a documentation technicality

It would be easy to read a PIL-versus-protocol mismatch as a paperwork inconsistency that doesn't affect the study itself. That undersells what's actually happening. A participant information sheet is the version of the study a participant actually experiences and consents to. If it describes a retention plan that differs from what the protocol specifies, either the leaflet is wrong about what the study will actually do, or the study's real practice has drifted from what was documented and approved. Neither is a good outcome, and both are more likely to surface as confused or frustrated participants partway through the study, rather than as a clean discrepancy someone catches in advance.

There's also a subtler cost. A participant who understood at consent that data collection would happen during a routine appointment, then finds themselves asked for a separate visit instead, has grounds to feel the study isn't quite what they signed up for. That's a retention risk in its own right, created not by the retention strategy itself but by the gap between what was promised and what was delivered.

What this suggests for how information sheets get produced

A few practical points follow directly from the data:

• A retention section in a PIL needs to be checked against the current protocol at the point of drafting, and again at any subsequent version. The mismatch rate found here strongly suggests these documents are often drafted from different starting points, or updated on different timelines, rather than kept in lockstep.
• Explaining why retention matters costs little and was mostly skipped. Fewer than one in fifteen leaflets connected retention to data quality or the study's ability to answer its question. That's a low-effort addition with a plausible upside for genuine engagement, not just compliance box-ticking.
• Version control between a protocol and its participant-facing documents is the actual fix, not better drafting discipline alone. If an amendment changes how retention will be handled, the systems producing participant materials need to reflect that change before the next participant reads the old version.

None of this requires participant information sheets to become longer or more technical. It requires the version a participant actually reads to be checked against the version the study is actually running, consistently, rather than assumed to already match.

It's also worth being honest about why this drift happens in the first place. Protocols and participant materials are often drafted by different people, on different timelines, sometimes months apart, and an amendment to one doesn't automatically trigger a review of the other. That's a process gap, not a case of anyone being careless. Treating a PIL and its protocol as a single linked pair, rather than two separate documents that happen to describe the same study, is a small shift in how documentation gets managed, and the mismatch rate found here suggests it's a shift most trial teams haven't made yet.