When does disability begin? Identifying the age of onset

Written by Daniel Mont

The age of onset for a disability, the age at which a disability becomes a dominant factor in a person’s life’ has ramifications for how that disability affects a person’s life. If a person is born with a disability it has an influence throughout the lifecycle, but conversely if a person becomes disabled late in life, while the effect on their life and their family members’ lives can be pronounced, many of their life outcomes will have been unaffected. A prime example is education. The educational outcomes of people whose date of onset was in their 60s will have nothing to do with barriers to education that people with disabilities faced during the time they were children.

For that reason, analysts may want to add a question to the Washington Group question sets about the date of onset. The first inclination may simply be to ask all people identified as having a disability using the WG questions (i.e. those answering “a lot of difficulty” or “cannot do” to one of the WG questions), “At what age did these difficulties begin?”

This is problematic for three reasons.

  1. People may not remember the exact age. This makes the question difficult for respondents to answer and can affect the conduct of the interview.  It will also cause measurement error that will be more pronounced if the analysis takes the exact age as given and specifically uses that in the analysis.
  2. The exact age may be difficult to determine. If a person is born with a disability or it occurs as the result of an accident or natural disaster, then the person may be able to remember the age with a fair amount of accuracy. But not all losses in functioning occur at a specific point in time. Some losses in functioning are gradual, because of aging or degenerative or worsening health condition. A person may gradually transition from having no difficulty seeing, to some difficulty, to a lot of difficulty. Thinking back in time it could be very difficult for someone to recall when the difficulties crossed those thresholds. What if a child’s difficulties were the result of malnourishment? At what point did that cause difficulties in functioning?
  3. People may have onsets of difficulties in different domains at different times. A person may have a congenital condition that makes it very difficult to walk and then later in life loses their eyesight. The onset of any disability occurred at birth, but the impacts of vision difficulties didn’t start until much later.

How can we best deal with these issues? For the first two issues, a good approach would be to not ask for a specific age (or date) but rather locate the part of the lifecycle in which a disability began. A possible question is to ask people saying they have a lot of difficulty doing on of the activities in the WG questions:

At what age did you start experiencing a lot of difficulty?

  1. From birth
  2. During childhood
  3. As a working age adult
  4. After I became an older adult

The exact wording of the responses would have to be developed and tested, maybe options c) and d) could be age ranges. However, the idea is to place the onset of the disability in the proper stage of life.  This will be useful for analysis. We would know, for example, if the person’s disability had an impact on their education (a or b) or their work outcomes (a, b, or c). People would most likely have fewer problems responding to such a question, and to do it accurately, as opposed to asking for an exact age.

The third issue – of multiple functional domains posing difficulties at different times – can be addressed by asking this question for each functional domain identified by the WG questions. The drawback, of course, is that this will add to the length of the questionnaire. It also may be annoying to the respondent if all of their difficulties began at the same time. “Why do you keep asking me?”

Therefore, a possible strategy for people who have a lot of difficulty in more than one domain is to ask the age when a lot of difficulty was first experienced.

Again, it will be important to cognitively test whatever formulation you use to be sure that the respondent understands and interpreting the question correctly so that the information gathered reflects the desired information.