26 May

Overall disability percentage calculation – its mathematics and inconsistencies

In our previous posts [link] [link], we focused on various challenges we face while working on issues in disability. In this post, we shall discuss how the overall percentage disability of a person is calculated by a medical board. Understanding this process sheds light on how people get scored a value which determines whether they receive pensions or not.

Another important reason for understanding this process is to question the inequity we notice in the assessments made on a daily basis by a medical board. We come across cases wherein two beneficiaries, with striking similarities in the nature of their disabilities, get assigned very different percentages. This is crucial because a person receiving a percentage of less than 40% is simply ineligible to avail the state’s pensions. And we do notice cases where people with similar symptoms are scored on either side of the 40% threshold. In such cases, we have no means to reason the differing assessment.

We refer to documents released by the Ministry of Social Justice and Empowerment which lay out the guidelines for assessing disability [1] [2]. In this post, we highlight the broader mechanism used to evaluate this percentage and also raise some concerns about its use on the ground. We focus on just the assessment of physical disability in this post.

Physical disability is identified and assessed in the upper and lower limbs of the body. The guidelines categorize each of the two limbs into components. For instance, the lower body is categorized into two main components – Mobility and Standing. Each such component is further divided into sub-components.

Quantifying sub-components
Each component generally is divided further into sub-components. For instance, the Arm component of the upper limb consists of sub-components like measuring the loss of motion, muscle strength, and coordinated activities. Likewise, the Hand component of the upper-limb involves measuring prehension, sensation, and strength. Each of these three sub-components, in turn, have sub-sub-components which need to be assessed. Various such sub-components and sub-sub-components are defined in the guidelines [1].

Consolidating various sub-components
One score can be given to a sub-component by consolidating values of each of its sub-sub-components. Some of these sub-sub-components are quantitatively assessed and some qualitatively. For instance, the Arm component of the upper limb contains loss of motion and muscle strength as sub-components. Loss of motion is defined quantitatively by averaging the loss in the three joints of the arm – shoulder, elbow and wrist. Each joint’s loss is measured by the percentage loss in angle of movement in the joint due to the problem. On the other hand, muscle strength is relatively qualitative, wherein a value between 0-100%, at an interval of 20%, is assigned to a joint based on physical inspection.

Consolidating components
In an attempt at quantifying and consolidating these various components, the following formula is provided to combine these different sub-components: CodeCogsEqn (6), wherein a and b are the scores of the various components. If a limb has more than two components, then the formula is repeatedly applied, in which the answer produced by the formula in one iteration becomes the value of ‘a’ in the next iteration.

An example
Here is an example of how one would compute the overall percentage disability for a person affected by Foot Drop, a case of polio affecting one’s foot, and a relatively common occurrence among those differently abled we facilitate —
The components defined for the lower extremity of the body are – Mobility and Stability. Mobility has Range of Motion and Muscle Strength defined as sub-components. This is how the values are quantified and consolidated –

Component 1: Mobility
Sub-component 1: Loss of range of motion (ROM)
Three joints – hips, knee, and ankle are evaluated. Each is weighted equally (30%, adding to a total 90%). We can assume the hips and knee are unaffected in this case. The disability of the ankle is quantified as –

Sub-sub-component Active ROM % Loss
Dorsiflexion 0 100%
Planterflexion full 0%
Inversion 0 100%
Eversion full 0%

Value for the total loss in ROM: CodeCogsEqn (1)

Sub-component 2: Muscle strength

Muscle strength is again calculated at three parts of the lower limbs – hips, knee and ankle. Assuming the hip and knee to be unaffected, the strength in the ankle is calculated as –

Sub-sub-component Strength (scale of 1-5) % Loss
Pl. flexors 5 0%
Dorsiflexors 0 100%
Invertors 0 100%
Envertors 5 0%

The values of 0 and 5 are provided based on visual inspection and the doctor’s expertise in assessing a score between 1-5. The total loss in muscle strength is then calculated as  –

CodeCogsEqn (2)

The combined value of mobility is calculated as  –

CodeCogsEqn (4)

Component 2: Stability

Let us assume that the stability component is unaffected in this case.

The overall disability percentage for the person would hence be 27.5%


As much as we appreciate the mechanism to make this process objective, we raise here some concerns in the manner in which its implemented on the ground.

Lack of transparency

Our biggest challenge on the ground is a lack of transparency in the calculation of the overall disability percentage. This calculation is not provided anywhere in the certificates that are finally handed out to the citizens. One in thirty citizens we facilitate ends up receiving a very different overall percentage as compared to another in spite of having similar symptoms to the other. The matter complicates in such cases. Our field team is left with no concrete information to appeal against such cases. To add to this woe, there exists no well-defined process to appeal for a re-evaluation. One has to speak to the doctors from the board and plead a case. They rarely agree to re-evaluate and even when they do, they agree to do so at a much later date. This adds to the inconvenience to the common man, given that s/he generally has to travel a good 20-50 km to visit the district hospital each time.

The right way to go about this is to publish this entire calculation and make it open to public scrutiny. In doing so, one is at least equipped with the right information to appeal a case. Neither is implementing such a process infeasible.

Validity and Random errors

There exist various sub-components in this evaluation system which still rely on non-quantitative methods of evaluation. Such a qualitative assessment could vary the overall score by a good number of points. For instance, in the example above, had the values of the muscle strength been rated 2 in each of the cases where it was 0, signifying a mild but prevalent issue, the overall percentage would have jumped to 30%. Such errors could then add up when consolidating scores from different components, greatly affecting the overall score. From an assessments viewpoint, the instruments used to assess metrics like muscle strength ought to be externally validated. There ought to be several well-established instruments which reliably assess such metrics.

In all, we do realize that there may not be a thoroughly objective way to replace these seemingly qualitative metrics, but we strongly believe this to be a research problem in itself. We believe that innovative assessment methods using low-cost technology like camera phones, sensors etc. can quantify the severity of specific conditions like muscle strength etc.

Systematic errors?

Using such a score to quantify disability warrants a careful study on any systematic errors that may be occurring. Doctors and medical boards may be systematically misinterpreting the formula in specific cases and assigning very different scores as compared to their peers in other boards. Assuming the overall distribution of the differently-abled population to be similar,  it is necessary to routinely look at numbers from different boards, districts, and states. This would identify systematic errors in the way the formula is interpreted and evaluated. Putting together this data is, however, an uphill task.

Why is the cut-off at 40%?

The reason behind selecting a cut-off score of 40% as the point of eligibility for pensions is not very clear. Nothing in the formula, to the best of our understanding, dictates setting such a value. Studying the distribution of percentages of every person evaluated for disability till date is of relevance when understanding the role of 40% as a threshold. This will reveal whether the 40% mark is leaving too many behind.

A silver lining

A silver lining in these cases is our field team has become well equipped. They’ve grown to possess a keen sense of what the overall percentage of a person would end up being. Consequently, they are fairly accurate in spotting when such a miscalculation has happened. We then work closely with such families in ensuring they visit the medical board on another day, giving them hope that they would be evaluated correctly!

Interested to know more about our work? Write to us at contact _at_ sevasetu.org


[1] http://www.ccdisabilities.nic.in/page.php?p=guide_others
[2] Explanations of the Guidelines and Gazette Notification of the Ministry of Social Justice and Empowerment, by Dr. Ratnesh Kumar et al. Link: http://niepmd.tn.nic.in/documents/Disability%20Evaluation.pdf


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