So it is exciting that the preamble to the new SDGs describes the need for inclusive development that leaves no one behind and that the document explicitly mentions disability 11 times, including in goals related to education, employment and inequality.  In addition, target 18 of goal 17 states that all programme data related to the SDGs must be disaggregated by disability, to monitor and ensure inclusion.
But how can we actually measure disability and whether people with disabilities are included in SDG-related development?
Unlike specific diseases that can be tested for via blood or urine tests, disability is a complex and umbrella term with many culturally different meanings. There are several models of disability. These include the medical model (disability is a problem with the individual’s body), the social model (disability is the barriers placed on an individual by society) and the prevailing biopsychosocial model (disability is the interaction between the individual’s health condition or impairment, activity limitations and external restrictions against their participation). 
This means that most of the limited data that exists on disability is based on non-comparable estimates that measure different attributes in different ways. Clinical tests of impairment (such as eye tests), reported activity limitations (“do you have difficulties seeing?”) and direct questioning (“do you consider yourself to have a disability”) are three examples. Research shows these measures provide very different estimates of disability and identify different groups.  For example, in India, 10.5 per cent of the population were identified as having a disability via clinical tests, 7.5 per cent via reported activity limitations and just 3.8 per cent via direct questioning.
“By having the right tools in place, we can monitor whether people with disabilities really are included in SDG-based programmes and policies. Only then can we ensure that, this time, they are not left behind.”
In light of this, the UK Department for International Development brought together politicians, academics and practitioners last year to agree on a comparable way to measure disability across programmes and settings.  Participants agreed to adopt a question set developed by the UN’s Washington Group on Disability Statistics when measuring disability inclusion in their own programmes, and to promote its use by others.
The questions target participants’ experience of activity limitations in six core functional areas, with answers ranging from “no difficulty” to “cannot do at all”.  They are simple, quick and easy to translate into different languages. They do not cause stigma, as they do not ask about disability directly. And, most importantly, using the same questions as part of monitoring disability inclusion in the SDGs would allow meaningful comparison between programmes and countries, and over time.
By having the right tools in place, we can monitor whether people with disabilities really are included in SDG-based programmes and policies. Only then can we ensure that, this time, they are not left behind.
Islay Mactaggart is a research fellow in disability and global health at the International Centre for Evidence in Disability, part of the London School of Hygiene & Tropical Medicine, United Kingdom. Before joining the centre in 2011, she worked for various disability and development organisations in Africa, Asia, the Caribbean and the Middle East. She can be contacted on [email protected] and is on Twitter @IslayMactaggart