Reliability and variability of physiotherapists scoring freezing of gait through video analysis

Background

The “gold standard” marker for freezing of gait severity is percentage of time spent freezing observed through video-analysis.

Objective

This study examined inter- and intra-rater reliability and variability of physiotherapists rating freezing of gait severity through video-analysis and explored effects of experience.

Methods
Thirty physiotherapists rated fourteen videos of Timed Up and Go performance by people with Parkinson’s and gait freezing. Ten videos were unique, while four were repeated. Freezing frequency, total duration, and percentage of time spent with freezing were computed. Reliability and variability were estimated using ICC(2,1) and mean absolute differences. Between-group differences were calculated with the one-way ANOVA.

Results
Inter- and intra-rater reliability ranged from moderate to good (ICC: Inter-rater– Frequency=0.63, Duration=0.78, Percentage=0.50; Intra-rater– Frequency =0.84, Duration=0.89, Percentage=0.50). Variability for freezing frequency was 2 episodes. Inter- and intra-rater variability for total freezing duration were 18.8 and 12.3 seconds respectively. For percentage of time spent with freezing, this was 15.2% and 13.5%. Physiotherapy experience had no effect.

Conclusion
Physiotherapists demonstrated sufficient reliability, but variability was large enough to cause changes in severity classifications on existing rating scales. Percentage of time spent with freezing was the least reliable marker, supporting the use of freezing frequency or total duration instead.