Need–Accuracy–Duration (NAD)
NAD makes explicit which decision warrants observation, what evidence is sufficient, and when observation should be reviewed. It is designed to simplify participatory debates on quantitative data between stakeholders with different levels of technical expertise.
- Need
- Who needs which information, for what decision, and with what consequences of error?
- Accuracy
- What measurement quality, temporal resolution and contextual information are sufficient?
- Duration
- How long is observation needed to capture uptake, stabilisation or discontinuation?
From an event to a testable hypothesis
Example: use of an assistive device declines. This could indicate burden, but also recovery, a different routine, additional support or a measurement error. Interpretation requires task context, self-report and specific comparison conditions.
For latent constructs, indicators, expected relationships and findings that would contradict a hypothesis should be specified in advance. A use measure is not equivalent to self-efficacy or disease progression.
Sensing on everyday objects
Capacitive grids and other object-mounted sensors can describe contact areas, changes of grip or use episodes. The CapGrid manuscript outlines such features for hand–object interaction. Their mapping to force, fatigue or cognitive load requires separate validation.
Related texts
- From Use Events to Value Signals: Establishing a Need–Accuracy–Duration Framework for Object-Centered Evaluation of Assistive Technologies
- Measuring long term use of assistive technologies with object mounted sensing: the Need-Accuracy-Duration framework
- Capacitive Grid Sensing on Everyday Objects: A Scalable Interface for Clinical Motor and Cognitive Monitoring
- Design als Rekalibrierung: Handfunktion, Dinggebrauch und die Iteration assistiver Artefakte