Counting disability: global and national estimation.

Purpose: How many people with disabilities are in the world? How is disability defined? How can we measure disability in an accurate and comparable way? These are some of the key questions which the recently published World Bank/WHO World Report on Disability (WRD) addresses.

Method: Multiple data sources and methods were used by WHO and the World Bank to estimate a global figure, with the ICF as the underlying data standard. Key international data sources were the World Health Survey of 2002-2004 and the 2004 updates from the Global Burden of Disease study. The World Report on Disability also includes a compilation of country-reported prevalence from census and surveys. This paper presents and discusses key findings of the Irish National Disability Survey (2006) to illustrate the value of the ICF framework for disability statistics and most especially the environmental factors component.

Results: The World Report estimates that globally one billion people or 15% of the world's population experience disabilities. Between 110-190 million people (2% of the world's population) experience severe or extreme difficulties in functioning. Definitions and measures of disability vary widely across countries. The Irish Disability Survey shows the substantial impact of environmental factors on people's functioning. For example, attitudes, and the presence or absence of facilitating equipment, support services, flexible working arrangements and transport significantly affect participation of people with disabilities in Irish society.

Conclusions: To improve the quality of disability information, the World Report recommends the use of a common definition and concepts of disability based on WHO's International Classification of Functioning Disability and Health (ICF). Furthermore, disability measurement needs to apply a multidimensional approach, in particular, measuring disability in terms of the level of difficulty a person is experiencing in multiple areas of life, rather than head counting severe impairment types in a dichotomous way. Environmental factors have significant effects on individual functioning and should be considered as an integral part in disability measurement.