Capability loss

For inclusive design, the range of user capabilities rather than disabilities is of most importance: high capability demands that exceed the capabilities of the users gives rise to design exclusion.

Figure: The prevalence of combined capability
The prevalence of combined capability
Losses shown are those for the Great Britain adult population (age 16+)

The figure above shows the overall capability loss segregated by age bands and severity levels (1-10 from slight to severe). It can be seen that frequency and severity of impairment increase with age. Gender differences are shown in the figure below.

Figure: Capability loss in Great Britain
Capability loss in Great Britain
Losses vary by age and gender across the population

Overall, the prevalence of capability loss increases with age for both genders, as would be expected. However, there are noticeable deviations from this trend in the 55-64 (around retirement age) and 75+ age bands for women and 60-69 (also around retirement age) and 75+ bands for men. The decrease in prevalence over the age of 75 is counter-intuitive. How could it have arisen?

Answer

The decrease in prevalence over the age of 75 arises from the sampling procedure of the survey. The survey was conducted with adults in domestic properties, not institutionalised care environment. As older adults develop severe impairments that make independent living more difficult, they are likely to move into retirement homes, thus removing themselves from the sample and biasing the results.

Multiple capability losses

The two disability surveys provide valuable information for analysing multiple capability losses, which are particularly important for design. Bubble diagrams provide a direct summary of capability distribution. The area of each circle represents a percentage of 16+ age band. The percentages of couplings between each pair of capability losses are shown in the plot.Fig 8.10).

Figure: Capability loss bubble diagrams
Capability loss bubble diagrams
Bubble diagrams show the coupling between motion, sensory and cognitive capability losses. The size of each bubble is proportional to the number of people with that pair of capability losses.

For example, it is evident that there is a high level of coupling (50% - represented by the circles within the blue square) between motion and sensory capability losses. The implication from the distribution of multiple capability losses for design is that focusing on accommodating individual capability losses may not necessarily include everyone with that loss, because some may still be excluded because of another capability loss.