Observer reactivity, also known as the 'Hawthorne effect', can roughly be described as the alteration of behaviour as a consequence of observation or awareness of measurement. Although researchers are aware of a potential observation effect during measurements, observer reactivity may also influence assessments that are performed as part of clinical care. Previous research on observer reactivity during gait measurements has resulted in contradicting outcomes and most studies examined the effects of participation in research rather than the clinical measurement of gait in a gait lab setting or the observation by professionals. Therefore, the aim of this study is to examine the differences in gait pattern between unobserved walking, observed walking, and observed walking combined with awareness of measurement, in a within-subjects repeated measures design.

Observer reactivity, also known as the 'Hawthorne effect', can roughly be described as the alteration in behaviour as a consequence of observation or awareness of measurement. It is believed that this could influence research outcomes in prospective experimental and observational studies. However, as described in a recent systematic review, the extend of the effect on research outcomes is still debated. The available studies on observer reactivity with various populations and tasks generate contradicting findings and conclusions. Especially within the health sciences, more research is necessary as observer reactivity may confound study results in the direction of better health outcomes.

Previous research on observer reactivity during gait measurements has resulted in contradicting outcomes. For example, some studies showed a higher walking velocity and better gait symmetry under observation, while others showed an opposite effect. This may be caused by the variation in diagnosis group between the studies or small sample sizes. Because of these mixed results and the low number of studies available on this topic, there is yet no consensus on a generalizable effect of observation during gait measurements. Furthermore, most studies examine the effects of participation in research rather than the clinical measurement of gait in a gait lab setting or the observation by professionals.

For clinical decision making, it is essential to investigate whether gait measurements are representative for the actual gait pattern of the patient. Therefore, the aim of this study is to examine the differences in gait pattern between unobserved walking, observed walking by a researcher, and observed walking combined with awareness of measurement by sensors.

Inclusion Criteria:

• Subacute or chronic stroke (>3 months ago)

Exclusion Criteria:

• Not able to walk 50 meters without resting.
• Not able to understand instructions given by the researcher.

The participants are masked to existence of different conditions, not to the measurement of their data.