Dr Shelley A Crawford, Professor
Occupational Therapist, Mater Hospital, Belfast
Deirdre M Walsh, Dr Alison P Porter-Armstrong
Health and Rehabilitation Sciences Research Institute, University of Ulster

Background: Pressure map interpretation has been described as a combination of art and science, suggesting that the visual interpretation of colour-coded pressure maps may be a subjective method of evaluation. The aim of this study was to determine if the visual ranking of pressure maps was reliable.

Methodology: Pressure maps were recorded from two disabled clients (Cases A and B) using the FSA pressure mapping system.  Cases A and B were pressure mapped on six seating surfaces at five time points.  The pressure maps were ranked from ‘best’ to ‘worst’ by student therapists (n=115) and by international experts (n=57). 

Results: High agreement was found between the visual ranking of the maps and maximum pressure values (W=0.873 to W=0.994).  Very high agreement was found between average pressures and visual ranking for Case B at four out of the five time points. High agreement was found between average pressure ranks and visual ranking for Case A at one time point only (W=0.788).  Therefore, it is likely that maximum pressure was easier than average pressure to extract as a benchmark for visual interpretation.  Perfect agreement was found for the modal ranking of pressure maps between the students and experts at three out of the five time points for Case A and four out of the five time points for Case B, demonstrating excellent inter-rater reliability at these time points.  High agreement for the visual ranking of pressure maps for Cases A and B at all time points was shown within the group of student (W=0.821 to W=0.938) and within the group of experts (W=0.875 to 0.944), thereby demonstrating high intra-rater reliability.

Conclusion: The visual interpretation of pressure maps has been found to be a reliable method for comparing seating surfaces for disabled clients, even when raters have limited experience.