Let’s do some math
Assume we’re designing an application and we don’t mind about accessibility.
As reported from The Colour Blind Awareness organisation:
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:
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 with the total number of people living worldwide, 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. 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.
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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.
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.