Since you already know that the prevalence of disability is around 15% worldwide, you're probably wondering what the proportions of various disability types are and which age groups they tend to effect, so you can focus on the most needed accessibility features first, right?
Sounds like a great idea, but there's just one problem: disability statistics are a mess.
Every now and them my job obliges me to look up all the latest disability figures for some presentation or another to convince a stakeholder that there actually is a user base for accessibility features and products. And I must admit I am equally frustrated by the venture every single time.
Sadly, there's no one good source of disability statistics. Different institutions usually only collect this kind of data once every few years. Various reports use different definitions of disability which make the data hard to compare. Some researchers only looks at formal disability (the criteria for which may differ significantly between countries), some use their own disability indicators (e.g. being able to walk a given distance or see newspaper print without a vision aid), others ask respondents for their subjective disability assessment. There's no consistency in dividing the disabled population into age groups, etc...
Despite all this, here are a few sources you should definitely consider on your quest for disability data:
- WHO disability website
- US Census disability reports
- American Community Survey
- Annual Disability Statistics Compendium website
- European Health Interview Survey
For the US population the disability rate in 2010 (the time of the last Americans with Disabilities report) was at around 19% and over 12% of Americans were severely disabled. Severe disability could mean being blind or using a wheelchair opposed to non-severe disabilities like "having difficulty seeing regular print" or "having difficulty climbing stairs".
As you may expect, disability is more common among the elderly. While there are only about 10% disabled Americans under 45, the figure skyrockets in older age groups going from just below 20% for 45-54 year-olds to a staggering 70% for over 80s.
Moreover, for the over 45 age groups the prevalence of severe disability steadily rises from around 13% for 45-54 year-olds to more than 55% for the over 80s.
Source: Americans with Disabilities 2010
The same report also provides some data on disability types.
Here the disability prevalence for various disability types is calculated for two age groups - all those over 15 and the elderly, i.e. people over 65 years of age.
By far the most common problem areas are motor function related: walking, standing and pulling (each approximately 10% and 30% for the respective age groups), lifting (7% and 21%), reaching (5% and 15%). Seeing and hearing disabilities were reported by a liitle above 3% over 15-year-olds and 10-11% over 65s. Also, notice, that something we take for granted like grasping is difficult or impossible to do for around 7.5% of elderly users!
Source: Americans with Disabilities 2010
Another survey, the US Census Bureau's American Community Survey distinguishes six basic disability types: hearing, vision, cognitive, ambulatory (motor disability), self-care and independent living. The "Americans with Disabilities" report also contained data for various everyday life activities (referred to as ADLs, i.e. activities of daily living) such as dressing, bathing or eating without assistance but did not address them jointly as a specific disability type. Although the self-care and independent living categories don't really convince me (they'll most commonly be a result of the respondent having various different disabilities at the same time which - combined - make him or her unable to live independently), they do provide some insights into disability prevalence.
According to the 2013 Survey's 1-year estimates, motor disabilities are once again the most common impairments in adult age groups, but in this report they effect just 5.2% of 18 to 64 year-olds and 23.3% of over 65s. The second most popular disability depends on the age group and is cognitive disability for the working age population and hearing and independent living disabilities for older adults. Poor vision is at the bottom of the list with 1.2% for younger adults and 6.8% among the elderly - way below the estimates given by the "Americans with Disabilities" report.
Hopefully, as time goes by, disability statistics will get better and more consistent. Oh, and just for the record, accessibility usage stats are even harder to come by. Pretty much the only thing we can say for certain is that the number of disabled people is steadily rising (mainly due to population ageing) and so is elderly users' technology awareness (after all, the grandads and grannies of tomorrow are going to be people who are already accustomed to using PCs, mobile phones and tablets) so the demand for accessibility aware design can only increase.
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