Anchors

An anchor is a per-participant reference date. Where a stage can be scheduled a fixed number of days after a participant joins, an anchor lets you schedule it relative to something that happens to that participant at their own time — the date they were randomised, their surgery date, their treatment start.

Every participant can hold a date for each anchor you define, and those dates are what stage schedules are calculated from.

Find them under Stages > Anchors.

When you need one

You need an anchor whenever "day 30" means thirty days after an event rather than thirty days after enrolment. Typical examples:

  • A surgical study where follow-up runs from the operation date, which differs for every participant.
  • A treatment study where the baseline is the first dose.
  • A study where participants are recruited over months but the schedule runs from a shared index event.

If everything in your study is scheduled from enrolment, you do not need anchors at all.

Creating an anchor

Click Add anchor and give it:

  • A name — required, and how you will pick it when scheduling stages. Name it after the event: "Surgery date", "Randomisation", "First dose".
  • A description — optional, but worth writing for whoever sets these dates in the clinic.
  • An assignment rule — how the date gets set for each participant.

Assignment rules

Rule Behaviour
Do not automatically trigger (manual only) Nothing sets it; a member of staff enters the date on the participant's record
When participant first logs in Set automatically the first time the participant opens the study
When a stage is completed Set automatically when the participant submits a given stage — optionally a specific recurrence or anchor slot of it

Automatic rules set the anchor to the moment the trigger occurred. They only ever fire once per participant: if a participant already has a date for that anchor, the rule does not overwrite it. That means a manually-corrected date is safe from being reset by a later trigger.

Setting a participant's anchor date

For manual anchors — and to correct an automatically-set one — open the participant's record and find the anchors section on their information page. Each anchor you have defined appears there with a date field. Set it, or clear it.

Setting a date immediately recalculates every stage scheduled against that anchor for that participant, so their schedule appears (or shifts) straight away.

Using anchors to schedule stages

Anchors do nothing on their own — they take effect through stages, in two places on a stage's Availability tab.

Anchor-scheduled stages. Choose Anchor-scheduled under Schedule stage, then add one slot per appearance: an anchor and a day offset. Offsets can be negative, so a pre-operative form can sit at day −7 while follow-ups sit at day 30 and day 90. Each slot appears to the participant as its own occurrence of the stage.

Make available after an anchor date. Under Stage availability, choose Make available after… and set the trigger to Anchor date, with an optional delay in days. The stage unlocks once the anchor is set and the delay has elapsed.

Until a participant's anchor date is set, stages that depend on it have nothing to schedule from and do not appear for that participant. This is normal — but it does mean a forgotten anchor date shows up as a participant with a suspiciously empty schedule.

Define anchors before you build the stages that use them. The stage editor can only offer anchors that already exist, and shows a warning where none are defined.

Editing and deleting

Editing an anchor's name, description or assignment rule is safe: dates already recorded against it are unaffected. Changing the assignment rule only affects participants who do not yet have a date.

Deleting an anchor is not safe, and Trialflare warns you before it happens. It removes every scheduled stage that depends on that anchor, and clears the anchor date from every participant. There is no undo. If stages are already scheduled against an anchor on a live study, repoint those stages first and delete the anchor afterwards.

Permissions

To do this You need
View and manage anchors on the Anchors tab Trial administrator — trial.admin, or trials.manage at team level
Set or clear an individual participant's anchor date trial.writeParticipantStudyData (or trial-wide write access)
Reference anchors when configuring a stage trial.write

See Roles and permissions.