Appendix B – Disability Severity Score
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Severity score
A severity score was developed using the Disability Screening Questions (DSQ). The method used to derive a score for each disability type and an overall score that takes all disability types into account is described below.
The score had to satisfy the following three criteria:
- it had to increase with the number of disability types;
- it had to increase with the level of difficulty associated with the disability;
- it had to increase with the frequency of the activity limitation.
Score for each disability type
Using a scoring grid that takes into account both the frequency of the activity limitations (never, rarely, sometimes, often, or always) and the intensity of the difficulties (no difficulty, some difficulty, a lot of difficulty, or cannot do), a score is assigned to each of the 10 disability types. The score increases with the frequency of the limitation and the level of difficulty. Hence, a person who reports always being limited in his or her activities and being unable to do an activity 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.
| Intensity of difficulty | Frequency of daily activity limitations | ||||
|---|---|---|---|---|---|
| Never | Rarely | Sometimes | Often | Always | |
| No difficulty | 0 | 0 | 2Note 1 | 3Note 1 | 4Note 2 |
| Some difficulty | 0 | 0 | 4Note 2 | 6Note 2 | 12Note 3 |
| A lot of difficulty | 0 | 3Note 1 | 6Note 2 | 18Note 3 | 20Note 3 |
| Cannot do | 0 | 4Note 2 | 12Note 3 | 20Note 3 | 24Note 3 |
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The score for each disability type is then normalized 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 normalized score for each disability type.
| Intensity of difficulty | Frequency of daily activity limitations | ||||
|---|---|---|---|---|---|
| Never | Rarely | Sometimes | Often | Always | |
| No difficulty | 0 | 0 | 0.0833Note 1 | 0.1250Note 1 | 0.1667Note 2 |
| Some difficulty | 0 | 0 | 0.1667Note 2 | 0.2500Note 2 | 0.5000Note 3 |
| A lot of difficulty | 0 | 0.1250Note 1 | 0.2500Note 2 | 0.7500Note 3 | 0.8333Note 3 |
| Cannot do | 0 | 0.1667Note 2 | 0.5000Note 3 | 0.8333Note 3 | 1.0000Note 3 |
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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.
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 above 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 disorders. 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 disorder have a score that is very low or 0. We therefore set a minimum score for people with developmental disorders. 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 five cases with developmental disorders.
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 overall 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, DHEA_CL for hearing, DMOB_CL for mobility, DFLE_CL for flexibility, DDEX_CL for dexterity, DPAI_CL for pain, DLEA_CL for learning, DDEV_CL for developmental, DEMO_CL for emotional, 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
Overall score
A person’s overall severity score is calculated by taking the average of the scores for the 10 disability types. Consequently, the more types of disability a person has, the higher his or her score will be. By definition, the overall 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 an overall score equal to the score for the “unknown” type divided by 10.
We created a variable for the overall score: DSCORE.
Overall severity class
To make the severity score easier to use, severity classes were established. 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; the latter have a less severe disability than people in class 3; and so on. We created a variable, DCLASS, for the overall severity class:
- 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 as very severe, 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. That corresponds to the score of a person who is in one of the most severe cells for one disability type, for example.
The breakdown of persons with a disability across the four severity classes is shown in the table below.
| Severity class | Persons with a disability |
|
|---|---|---|
| number | % | |
| Class 1 = mild | 1,195,590 | 31.7 |
| Class 2 = moderate | 747,980 | 19.8 |
| Class 3 = severe | 849,540 | 22.5 |
| Class 4 = very severe | 982,810 | 26.0 |
| Source: Statistics Canada, Canadian Survey on Disability, 2012. | ||
Overall score for persons without a disability in the CSD
In the CSD’s sample (the YES sample), there are two types of people without a disability:
- People interviewed for the CSD who reported being limited only "rarely� with "no difficulty� or "some difficulty�. For the purposes of the CSD interview, these people were deemed potentially to have a disability and therefore had to answer all the survey questions. However, they were excluded from the final definition of disability.
- People interviewed for the CSD who reported that they were "never� limited (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.
We calculated an overall score for the people without a disability in group (a), but the people in group (b) all have a score of 0. Since CSD data are available for the people in group (a), users may want to study their characteristics and try to compare the severity of the group’s members among themselves, even though all these cases are very mild. The number of points used to calculate the scores of these persons was intentionally set very low to ensure that people who reported being “rarely” limited with “no difficulty” or “some difficulty” for several types would not end up with a higher score than someone who is considered to have a disability under the definition used in the CSD.
| Intensity of difficulty | Frequency of daily activity limitations | ||||
|---|---|---|---|---|---|
| Never | Rarely | Sometimes | Often | Always | |
| No difficulty | - | 0.1 | - | - | - |
| Some difficulty | - | 0.2 | - | - | - |
| A lot of difficulty | - | - | - | - | - |
| Cannot do | - | - | - | - | - |
| Source: Statistics Canada, Canadian Survey on Disability, 2012. | |||||
Again, the score for each disability type is then normalized to a value between 0 and 1 by dividing it by the maximum score of 24. The table below shows the normalized scores of people who are considered not to have a disability but answered all of the CSD question.
| Intensity of difficulty | Frequency of daily activity limitations | ||||
|---|---|---|---|---|---|
| Never | Rarely | Sometimes | Often | Always | |
| No difficulty | - | 0.0042 | - | - | - |
| Some difficulty | - | 0.0083 | - | - | - |
| A lot of difficulty | - | - | - | - | - |
| Cannot do | - | - | - | - | - |
| Source: Statistics Canada, Canadian Survey on Disability, 2012. | |||||
It is important to note, however, that for people without a disability in group (a), even though we had to calculate a score for each disability type to obtain the overall score, the score for each type was then reset to 0 in the final file. The number of disability types was also set to 0. This is to avoid any confusion when the types of disability are studied, since these people should not be counted as having a disability.
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