Let’s do some math

Developers and designers usually think that the of their application is 100% healthy and because of that they imagine accessibility not related to usability.

Assume we’re designing an application and we don’t mind about accessibility.

Some statistics

Color blindness

As reported from The Colour Blind Awareness organisation[1]:

Colour (color) blindness (colour vision deficiency, or CVD) affects approximately 1 in 12 men (8%) and 1 in 200 women in the world.

Given m = “ratio of men”, the percentage of users who are color blind and use your application is roughly b = m * 8% + (1 – m) * 0.5%.
In the worst scenario where you don’t mind about accessibility and almost every person who uses your app is a man, 8% of those people can’t use it properly.


According to the World Health Organization[2]:

About 15% of the world’s population lives with some form of disability

Assuming that the distribution of people with disabilities in the world is the same as your target, 15% of them will have problems using it.


If we divide the number of population aged 65 and above[3] with the total number of people living worldwide[4], we get a range of elderly people higher than 8%.

When we’re designing a website or building a shiny Android application we have to keep in mind that these users have not necessarily a disability or a disease, but usually they see worse, they have less control of their body (e.g. difficulties while using the mouse or the touchscreen) and so on.

We also know that 46% of older people (those aged 60 years and over) have disabilities[5]. With this data, we can estimate P(G ∪ A).
P(G ∪ A) = P(G) + P(A) – P(A ∩ G) = 15% + 8% – 3% = 20%.

Nota bene: it’s just an estimate because we don’t have data about the number of people with disabilities aged 65 and over. I also assume that the distributions from the data set are the same as the future users of the application.


Designing an application which is accessible will allow you to have a wider userbase.


All links were visited on 19 august 2018.
If one link will be broken, consider using https://web.archive.org/.

[1] http://www.colourblindawareness.org/colour-blindness/

[2] http://www.who.int/disabilities/world_report/2011/report/en/

[3] https://data.worldbank.org/indicator/SP.POP.TOTL
Other references: ( 1 ) United Nations Population Division. World Population Prospects: 2017 Revision. ( 2 ) Census reports and other statistical publications from national statistical offices, ( 3 ) Eurostat: Demographic Statistics, ( 4 ) United Nations Statistical Division. Population and Vital Statistics Reprot ( various years ), ( 5 ) U.S. Census Bureau: International Database, and ( 6 ) Secretariat of the Pacific Community: Statistics and Demography Programme.

[4] https://data.worldbank.org/indicator/SP.POP.65UP.TO
Other references: World Bank staff estimates using the World Bank’s total population and age/sex distributions of the United Nations Population Division’s World Population Prospects: 2017 Revision.

[5] https://www.un.org/development/desa/disabilities/disability-and-ageing.html

Source link https://blog..io/the-average-user-has-disabilities-c64233a7f2a4?source=rss—-eb297ea1161a—4


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