Participant Management

The Participants tab

Open a study in the Study Builder and choose Participants in the top row of tabs. The tab has three sub-tabs:

• Participant Management: study length, sample size, recruitment dates, group assignment, participant codes, completion rules and settings for what participants see in the app.
• Informed Consent: the consent text shown during onboarding.
• Prescreening: an optional questionnaire shown before consent.

Changes are stored when you click Save in the Study Builder header. For a study that is already running, see Study Management for how changes reach participants.

The Participants tab as a video

A narrated walkthrough (4:24) of the tab in the study from the quickstart video: study length, sample size planning and recruitment dates, rule-based groups with Pocock–Simon minimization, participant codes, automatic completion, the study information settings, informed consent, and an eligibility question in prescreening. It is filmed in SMAAT on the Free plan. The narration is a synthetic voice; turn on captions in the player to read along.

Recorded in October 2026. Screens in newer versions of SMAAT may differ slightly. Chapters, transcript and all video tutorials →

Study length

Length of Study takes a number and a unit (Minutes, Hours, Days or Months). It is the duration of participation for each participant, counted from that participant's enrollment. The value is used for event-based notifications that fire when the study ends for a participant, such as a debriefing survey. It is also shown to participants in the app and on the public study page.

Sample size planning

The Sample Size Planning section has the field Planned number of participants, which records how many participants the study aims to recruit. The button Plan sample size opens the Power & Design Planner at power.smaat.eu in a new tab. The study length and the notification schedules of the study's surveys are passed to the planner. For schedules with a fixed number of prompts per day (fixed times, random sampling, intervals), the daily number of prompts is passed as well. For event-, geofence-, place-visit- and sensor-triggered schedules, the number of prompts per person varies at random, and the expected average rate is entered in the planner.

When the planner sends a recommended sample size back, the Study Builder reopens on the Participants tab and shows the notice "Applied a planned sample size of N from the Power & Design Planner". The value is written into Planned number of participants. Click Save to keep it.

Recruitment dates

The Recruitment Strategy section starts with Recruitment Start Date and Recruitment End Date. When both dates are set, the app shows them on the study information step of onboarding, and they appear on the public study page. The dates are information for participants. To open or close a study on a given date, use the scheduled status changes described in Study Settings.

Assignment to groups

A group code labels a participant as a member of a group, for example an experimental condition. Each survey has a Group Code field (Study Builder → Protocol → Surveys). A survey with a group code is sent or shown only to participants with that code; a survey without one goes to all participants. The select Assignment to Groups offers seven options:

• Do not assign: participants receive no group code.
• Assign to a specific group: every new participant receives the code entered under Group Code.
• Assign based on join time: each row has a Group Code, a Start Date and Time and an End Date and Time. Rows are added with Add More Options, and a timeline preview shows the windows. A participant who joins inside a window receives its code. If windows overlap, one of the overlapping codes is chosen at random. A participant who joins outside every window receives no code.
• Assign based on rules: a table of group codes with a Probability (%) each, edited with Add Rule. The probabilities must sum to 100%. A pie chart shows the planned distribution.
• Allow participants to enter their group code: participants type a code during onboarding, guided by the text in Instructions for Participants. The editor warns that participants may mistype the code.
• Allow participants to select their group code: participants choose one code from the list under Selectable Group Codes.
• Assign based on prescreening answers: the code is derived from answers to the prescreening questionnaire (see below).

A group code included in a personal invitation takes precedence over the assignment option.

Pocock–Simon minimization

With Assign based on rules, each participant is allocated by chance according to the probabilities. With small samples, chance allocation can produce groups of unequal size. The checkbox Use Pocock–Simon minimization switches to minimization, an adaptive allocation method. For each new participant, the server computes which group assignment would bring the current group proportions closest to the target probabilities. Participants with the status Enrolled or Completed are counted. A biased coin then assigns the participant to that group with the Bias probability and otherwise allocates by the target probabilities. The slider ranges from 0.50 to 1.00 (0.80 is marked as recommended; 1.00 always picks the balancing group, which makes the sequence predictable). Balancing uses group counts only. Participant characteristics are not taken into account.

Assignment from prescreening answers

This option requires prescreening questions; if there are none, the editor asks you to add them in the Prescreening sub-tab first. Each rule has a group code under Assign to group code, one or more conditions on prescreening questions, and a condition logic: All conditions must match (AND) or Any condition must match (OR). Rules are checked in order, and the first matching rule applies. Participants who match no rule receive the code in Fallback group (if no rule matches), or no code if that field is empty. Assignment runs when the participant completes prescreening.

Participant code assignment

Each participant has a participant code that identifies them in the dashboard and in data exports. The select How should participant codes be assigned? offers two options:

• Generate random participant code: the server creates a code of five characters from the letters A–Z and the digits 0–9, for example K7Q2M.
• Let participant enter their participant code: participants type their own code during onboarding. The text in Instructions for Participants tells them how to form it, for example from initials and a four-digit number.

The setting applies to participants who join without a personal code, for example with the general study code. Personal invitations carry a predefined participant code, which is used instead. Codes can be edited later on the study's Participants page; see Study Dashboard.

Study completion rules

With Enable automatic study completion, the server sets a participant's status to Completed once two kinds of conditions are met:

• Minimum Days Participated: the number of full days since enrollment (0 for no minimum).
• Required Survey Completions: for each selected survey, a minimum number of submitted responses. Rows are added with Add Required Completion, and all rows must be met.

The check runs each time the participant submits a survey response. Completed participants move to Previous Studies in the app. The status can also be set by hand on the study's Participants page.

Study information settings

Three checkboxes control what participants see and must do in the app. The first two are off by default; the third is on.

• Show participants all scheduled surveys: the Surveys tab of the app lists upcoming prompts as well. When the box is off, participants see only prompts whose time has come. Leave it off for random schedules, so that participants cannot anticipate prompt times.
• Require participants to enable all required permissions before joining the study: onboarding cannot continue past the permissions step until every permission the study needs (notifications, sensors) is granted. When the box is off, participants can join and grant permissions later.
• Allow participants to visualize their survey data over time in the app: the study screen in the app shows a My Data button with charts of the participant's own submitted responses.

Participant limits per plan

The number of participants per study depends on the plan of the study's author:

Every participant on the study's list counts, whatever their status. Participants moved to Removed participants do not count. When the limit is reached, the server refuses new joins, and the app shows: "This study isn't accepting new participants right now. Please contact the research team." Participants already enrolled are not affected.

Informed consent

The Informed Consent sub-tab has seven fields:

1. Nature, Purpose, and Duration: objectives, the data collected, the reason for the study and the duration of involvement.
2. Procedures, Risks, and Benefits: the tasks participants perform, risks and their mitigation, and benefits.
3. Confidentiality and Data Handling: how data are protected and handled.
4. Point of Contact: a contact for participants.
5. Withdrawal Process: how to withdraw and what happens to the data.
6. IRB Approval Number: the approval number of the ethics committee (IRB, institutional review board).
7. IRB Institution: the institution that issued the approval.

In the app, the consent step of onboarding shows each field as a separate section, followed by the I Agree button. A section left empty is shown as "No information provided" ("No contact information provided" for the point of contact, "No IRB approval information provided" when the approval fields are empty). Participants can still agree and join. The same sections remain available to participants on the study's Info screen after joining.

Empty consent fields do not block activation. When Validate & Activate runs, a missing IRB approval number and a missing IRB institution each produce a warning ("… recommended before activating").

Explicit consent for sensitive data

If the study collects precise location (GPS), motion sensors (accelerometer, gyroscope, magnetometer, barometer, pedometer, device motion, light) or health data, the consent step adds a separate checkbox for explicit consent to these special categories of personal data (GDPR Art. 9). Participants cannot continue until it is ticked.

Time commitment

The study's Burden tab can generate a statement of the expected time per day. Its button Add to informed consent appends a line starting with "Time commitment:" to Nature, Purpose, and Duration and shows the figure in a Time commitment block on the consent step in the app.

Prescreening

Prescreening is a short questionnaire shown during onboarding, after the study overview and before consent. It is switched on with Enable prescreening in the Prescreening sub-tab. Questions can be added with Add question or from ready-made items with Browse templates. The editor has four sections.

Eligibility

Eligibility questions decide whether a person may join. Two question types are available. An Eligibility Question has rules on the answer (for example, age greater than or equal to 18). A Risk Acknowledgement must be answered "Yes". Under Eligibility Policy, the rule evaluation is either All eligibility questions must pass (strict) or At least one eligibility question must pass (lenient). The answers are checked on the server.

• Message shown to ineligible participants: the text that people who do not qualify see in the app.
• Offer a waitlist to turned-away participants: people who fail eligibility, or who are turned away by the enrollment cap, can leave an email address with Join waitlist. The waitlist appears in the same section of the editor; each entry has a status (Pending, Contacted, Enrolled, Dismissed) and internal notes.
• Enrollment Cap: with Stop accepting new participants once target is reached, new applicants who pass eligibility are turned away once the number of Enrolled participants reaches the target. They see the cap message. Enrolled participants are not affected.

Baseline

Baseline measurements are collected at enrollment: demographic questions, validated scales, device and technology checks, engagement or commitment questions, and open questions. Templates come from the Item Library, so a module such as Core Demographics adds all of its questions at once. The answers appear in a prescreening panel on each participant's Details page.

Quiet time

With Enable quiet time, participants state periods in which they do not want notifications. Three pickers can be switched on, each with its own question text: Time of day window (for example 22:00 to 07:00, overnight windows allowed), Days of week and Calendar date ranges (for example a holiday). Notifications that fall into a participant's quiet time, evaluated in the participant's time zone, are not delivered on any channel. The survey itself stays visible in the app. The Notifications page marks such rows with a quiet-time indicator.

Events

The Participant-Defined Events section collects scheduling anchors from participants: Preferred Notification Time, Wake / Sleep Time, Preferred Days of Week and Calendar Event (one or more dates, such as clinic visits). Each answer type matches a trigger of the event-based notification schedule under Prescreening-based, for example "Participant's Preferred Time". A calendar-event trigger sends one notification per entered date. See Designing Surveys for event-based schedules.

Next steps