Designing Behavioural Prompts That Work

Most digital trials include reminders. Notifications prompt participants to complete diaries, attend visits or take supplements. But not all reminders are equal. Some quietly encourage behaviour. Others irritate or confuse. And a few do the opposite of what they were meant to do.

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The difference often comes down to how the prompt is written and timed. It also depends on whether it functions as a nudge or a notification. These are not the same.

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A notification is a message. It provides information. “Your diary entry is now available.” “Reminder: complete your Day 10 questionnaire.” The tone is usually neutral and direct. These are necessary. But on their own, they rely on the participant to act without added motivation.

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A nudge is something different. It is a behavioural design choice that makes the desired action easier, more appealing or more automatic. Nudges are often invisible. The most effective ones feel like part of the process, not an interruption.

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For example, instead of sending a plain notification at 6pm, a study app might:

• Display a progress bar showing how close the participant is to finishing their weekly tasks
• Use a notification that includes a reassuring message like “You’re nearly done for the day”
• Time the reminder to appear just after typical mealtimes, when participants are more likely to be reflective and receptive

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These changes sound minor, but they often produce higher completion rates with less frustration.

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There is also a psychological layer. Messages that suggest progress and participation tend to perform better than those that imply failure or obligation. Compare:

• “You haven’t completed your last three diary entries”
• “Thanks for what you’ve submitted so far. Your next diary entry is ready when you are”

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The second message avoids shame. It invites the participant back in without scolding them. In long studies especially, tone matters more than many teams realise.

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Behavioural prompts work best when they are:

• Timed around natural routines (like waking, eating or winding down)
• Short, clear and kind in tone
• Designed to reduce the number of steps needed to complete the task

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That might mean linking directly to the task instead of opening the app home screen. It might mean sending a gentle reminder if a task was started but not submitted. It might mean switching to email or SMS if the app has been ignored for a few days.

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A nudge can also take the form of interface design. A task that is pre-filled with yesterday’s value (with the option to change it) may feel less demanding than a blank form. A calendar that shows completed days builds a habit loop without needing words.

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It helps to test these ideas. Small pilots can show which message timings and formats work best. These results often vary by population. A student group may respond well to early evening prompts. Retirees might prefer mornings. A nutrition study may benefit from pre-meal nudges, while a mental health study may see better results from bedtime reflections.

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The point is not to build perfect behaviour. It is to reduce the number of things standing between the participant and the next completed task. That means using reminders, yes, but also considering the emotional tone, the timing and the friction involved.

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Nudges are subtle. But over the course of a study, their effect can be anything but small.

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