5. Severity score^{Note 1} A New Survey Measure of Disability: the Disability Screening Questions (DSQ)
5. Severity score^{Note 1}

One of the goals of the DSQ was to make it possible to calculate a severity score. For each disability type, data are collected on the intensity of the difficulty and on the frequency of activity limitations, which can be combined to compute a global score. The score had to satisfy the following three criteria: it had to increase with the number of disability types; increase with the level of difficulty associated with the disability; and increase with the frequency of activity limitation.

The method used to calculate a severity score for each disability type and the global score that takes all types into account, is described below. The score was developed with the data from the 2012 CSD.

5.1. Score for each disability type

Using a scoring grid that takes into account both the frequency of activity limitations (“Never,” “Rarely,” “Sometimes,” “Often,” or “Always”) and the intensity of difficulties (“No difficulty,” “Some difficulty,” “A lot of difficulty,” or “Cannot do”), a score is assigned to each disability type (Table 5A). The score increases with the frequency of the limitation and the level of difficulty. Hence, someone 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.^{Note 2} In the grid, the most severe responses have higher scores, moderate responses have mid-range scores, and mild responses have lower scores. The designation of severe, moderate and mild responses is not the same as the overall severity class description in Section 5.4; this is only a way of qualifying the combination of answers for a given type.

The score for each disability type is then normalized to a value between 0 and 1 by dividing the score in each cell by the maximum score, which is 24 (Table 5B).

Special cases

The scoring grid was used for most disability types, but was adapted in 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. Because, by definition, respondents with an “Unknown” type have only one type of disability, the intensity distribution for other respondents who had only one of the 10 disability types was examined. In most cases, the intensity level was “Some difficulty.” Hence for the “Unknown” type, the scoring grid (Table 5B) was used, and the intensity level was set at “Some difficulty.” “Sometimes” responses were given 0.1667 points; “Often” responses, 0.25 points; and “Always” responses, 0.50 points.

The second special case was developmental disorders. Someone reporting this disorder is automatically deemed to have a disability, regardless of the level of difficulty and frequency of limitations. To avoid situations where people with a developmental disorder have a score that is very low or 0, a minimum score was assigned based on the grid. If the reported frequency of the limitation was “Never,” or “Rarely” combined with “No difficulty” or “Some difficulty,” the score was set to 0.0833 (the minimum for any other disability type). A minimum score was assigned in about one of every five cases of developmental disorders.

The third special case pertains to the “mobility” and “flexibility” disability types, for which two questions are asked about the intensity of the difficulty, rather than one. To calculate the severity score for these two types, the higher intensity reported on the two questions was used, combined with the frequency of the limitation. The higher intensity for the two questions (rather than an average) was chosen because it was preferable for each of the 10 disability types to have the same importance in the calculation of the overall score. The need for two questions to establish if a respondent has mobility or flexibility difficulty should not lower that person’s score when the answer to one question is “No difficulty” and the answer to the other is “Cannot do,” for example.

5.2. Severity class for each disability type

For each disability type, two severity classes were defined: 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 for this type; others are assigned to the less severe class. People scoring 0 for a type are classified as not having that disability type.

In the CSD analytical file, variables for the severity class of each disability type were created (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 mental health-related, 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

5.3. Overall severity score

The overall severity score takes into account every disability type that a person has. It is the average of the scores computed for the 10 disability types. Consequently, the more types of disability a person has, the higher the score. 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 (“unknown” type) have an overall score equal to the score for the “Unknown” type divided by 10.

In the CSD analytical file, a variable for the overall score was created: DSCORE.

5.4. Overall severity class

To make the severity score easier to use, severity classes were established. The name assigned to each class is intended to facilitate its use; it is not a label or judgment about an individual’s level of disability. 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. In the CSD analytical file, a variable, DCLASS, was created for overall severity class:

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

The cut-off point between classes 2 and 3 was first determined graphically. A natural discontinuity in the distribution of the overall score is apparent near the value of 0.1. This value corresponds to the score of a person who received the maximum number of points for a single disability type, which puts the person in the severe class. To be classified as very severe, a person has to have double that score, or 0.2, which corresponds to the score of a person who would have received the maximum number of points for two disability types, for example. The cut-off point between class 1 and class 2 is half the score required for class 3 (0.05), which is the score of a person in one of the most severe cells for one disability type, for example.

The distribution of persons with a disability across the four severity classes in the 2012 CSD is shown in Table 6.

5.5. Overall score for persons without a disability (2012 CSD only)

Typically, persons without a disability would have an overall severity score of 0, but an exception was made for the 2012 CSD. As noted previously, when the CSD was sent to the field for collection, the final decision on who would be considered a person with a disability (should the “Rarely” answers be included?) based on the DSQ had not been made. Therefore, people who were only rarely limited had to complete the entire CSD interview even though they might ultimately be considered not to have a disability.

A score was computed for these respondents so that their characteristics could be studied. This group is called “Soft Rarely”—they reported being limited “Rarely” with “No” or “Some” difficulty. Respondents who reported “Never” being limited (except those with a developmental disability) have a score of 0.

The number of points used to calculate the scores for the “Soft Rarely” was deliberately set very low to ensure that people who reported being “Rarely” limited with “No” or “Some” difficulty for several disability types would not receive a higher score than someone considered to have a disability under the CSD definition. The points assigned to these responses are shown in Table 7A.

The score for each disability type is normalized to a value between 0 and 1 by dividing it by the maximum score of 24 (as shown in Table 5A). Table 7B shows the normalized scores for persons reporting “Soft Rarely” disabilities.

For the “Soft Rarely” group, even though a score for each disability type had to be calculated to obtain the global score, the score for each type was reset to 0 in the final file. The number of disability types was also set to 0. This is to avoid confusion when examining a specific disability type, since the “Soft Rarely” should not be considered as having a disability.

• Previous
• Next