Canadian Survey on Disability, 2017: Concepts and Methods Guide
Appendix C – Disability severity indicators

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Severity scores and classes

Severity scores were developed using the Disability Screening Questions (DSQ). The method used to derive a score for each disability type and a global score that takes all disability types into account is described below.

The scores had to satisfy the following three criteria:

• it had to increase with the level of difficulty associated with the disability;
• it had to increase with the frequency of the activity limitation;
  and for the global score:
• it also had to increase with the number of disability types.

In order to facilitate usage of the severity scores, severity classes were established for each disability type and at the global level.

Score for each disability type

Using a scoring grid that takes into account both the intensity of the difficulties (no difficulty, some difficulty, a lot of difficulty, or cannot do) and the frequency of the activity limitations (never, rarely, sometimes, often, or always), a score is assigned to each of the 10 disability types. The score increases with the level of difficulty and the frequency of the limitation. Hence, a person who reports being unable to do an activity and always being limited in his or her activities will have the maximum score for that disability type. The scoring grid developed for each disability type is shown below. In the grid, the most severe responses have higher scores, moderate responses have mid-range scores, and mild responses have lower scores.

The score for each disability type is then standardized to a value between 0 and 1. This is done by dividing the score in each cell by the maximum score of 24. The table below shows the standardized score for each disability type.

Special cases

The scoring grid shown above was used for the majority of the disability types, but it had to be adapted for three special situations: the unknown type, developmental disabilities and the mobility and flexibility types.

First, the DSQ had no questions on the intensity of the difficulty for the unknown type. Consequently, only those who reported being limited “sometimes”, “often” or “always” were considered to have a disability. Since, by definition, people in the unknown type have only one type of disability, we examined the intensity distribution for other people who had only one of the 10 disability types. We found that in most cases, the intensity level was “some difficulty”. For the unknown type, therefore, we used the scoring grid shown in Table C.2 and set the intensity level at “some difficulty”. The “sometimes” responses were hence given 0.1667 points, the “often” responses 0.25 points, and the “always” responses 0.50 points.

The second special case concerns developmental disabilities. For this disability type, a person who reports being diagnosed with this disorder is automatically deemed to have a disability, regardless of the level of difficulty and the frequency of the limitations reported. However, in calculating a score for this type, we want to avoid situations where people with a developmental disability have a score that is very low or 0. We therefore set a minimum score for people with a developmental disability. We use the grid to determine the score, but if the reported frequency of the limitation is “never”, or if it is “rarely” combined with “no difficulty” or “some difficulty”, we set the score at 0.0833, which is the minimum score that a person can have for any other disability type. We assigned a minimum score in about one of every six cases of persons with a developmental disability.

The third special case relates to the mobility and flexibility types. For these two types, we have two questions on the intensity of the difficulty, instead of just one question. To calculate the score for these two types, we used the higher intensity reported on the two questions, combined with the frequency of the limitation, to determine the score. The decision was made to use the higher intensity for the two questions, rather than an average value for example, because we wanted each of the 10 disability types to have the same importance in the calculation of the global score. The fact that we needed two questions to establish whether the respondent has difficulty for mobility or for flexibility should not lower the person’s score when the answer to one question is “no difficulty” and the answer to the other is “cannot do”, for example.

Severity class for each disability type

For each disability type, we define two severity classes: less severe and more severe. People with a score of 0.5 or more for a disability type are assigned to the more severe class, and others are assigned to the less severe class. People with a score of 0 for a disability type are classified as not having that disability type.

We created a severity class variable for each disability type: DVIS_CL for seeing, DHEAR_CL for hearing, DMOB_CL for mobility, DFLEX_CL for flexibility, DDEX_CL for dexterity, DPAIN_CL for pain, DLRN_CL for learning, DDEV_CL for developmental, DMENT_CL for mental health, DMEM_CL for memory, and DUNK_CL for unknown. Each variable takes one of the following values:

• 0 = no disability
• 1 = less severe
• 2 = more severe

Global score

A person’s global severity score, DSCORE, is calculated by taking the average of the standardized scores for the 10 disability types. Consequently, the more types of disability a person has, the higher his or her global score will be. By definition, the global score is also a number between 0 and 1. People who report no disability for the 10 types but report another health problem or condition (i.e., they have an unknown type) have a global score equal to the standardized score for the unknown type divided by 10.

Global severity class

To make the global severity score easier to use, global severity classes were established (variable DCLASS). It is important to understand that the name assigned to each class is simply intended to facilitate its use. It is not a label or judgement concerning the person’s level of disability. In other words, the classes should be interpreted as follows: people in class 1 have a less severe disability than people in class 2; people in class 2 have a less severe disability than people in class 3; and people in class 3 have a less severe disability than people in class 4.

• 1 = mild disability
• 2 = moderate disability
• 3 = severe disability
• 4 = very severe disability

The cut-off point between classes 2 and 3 was first determined graphically. There is a natural discontinuity in the distribution of the overall score near the value of 0.1. In fact, this value corresponds to the score of a person who received the maximum number of points for a single disability type. That would put the person in the severe class. To be classified among the very severe disabilities, a person has to have double that score, or 0.2. A score of 0.2 corresponds to the score of a person who received the maximum number of points for two disability types. The cut-off point between class 1 and class 2 is half the score required for class 3, i.e., 0.05. This value corresponds to the score of a person who received middle-range points for a single disability type, for example, or lower-range points for multiple disability types. That would put the person in the moderate class.

The breakdown of persons with a disability across the four severity classes is shown in the table below.

Global score for persons without a disability in the CSD

In the CSD’s sample (the YES sample), people without a disability are: people interviewed for the CSD who reported that they were “never” limited as well as those who reported being limited only “rarely” with “no difficulty” or “some difficulty” (called “false positives”). For the purposes of the CSD interview, these people were deemed not to have a disability and therefore did not have to answer the rest of the survey questions. Persons without a disability all have a global score of 0^Note .

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