Important decision from the Supreme Court regarding combining of multiple impairment scores
A case was recently heard in the Supreme Court that dealt with the issue of how to combine numbers when using the 4th Edition of the AMA Guides to the Evaluation of Permanent Impairment.
The decision of Justice Beach in the matter of Weigert v TAC was delivered on 5 November 2010.
Some might be aware that it was Justice Beach who also presided in the other important case from earlier this year which also dealt with the issue of how to combine numbers when using the guides (Nicholls v Corlett & Ors)
Both of these cases were about how to combine three or more numbers when using the Guides, and whether the combined values chart or the combining formula should be used.
In the Nicholls decision, Justice Beach said that when combining multiple impairments, “the most rational approach may be to apply the formula A + B (1-A) to achieve a precise figure – and one that will not vary depending on which figures are chosen in what order”.
In Weigert, Justice Beach held that the formula should be used because “the application of the formula in multiple impairment cases produces precision, certainty and consistency”.
So what does this mean for Accredited Impairment Assessors conducting assessments for the TAC, Worksafe and Wrongs Act?
Where there are three or more impairments that need to be combined then the scores should be put together using the combining formula.
An easy way to apply the combining formula is simply to click on this link which will take you the ‘combined values calculator’ in the Newsletters section of the Impairment Assessment Training website. You can then enter the numbers that you need to combine into the calculator and it will do the mathematics and work out the combined score.
Alternatively, examiners may simply confirm each impairment score that they wish to give, and leave it to the TAC or WorkSafe to calculate the overall impairment score by using the formula.
How to select a score within a class?
A question that is often asked during the training programme is how to decide what percentage impairment to give when the Guides indicate that a range may be appropriate. Many tables in the Guides indicate that there are a number of potential classes into which the impairment may fall and in each class a range of impairments may be provided. The Guides in general are not explicit as to how one should choose a particular score within the range for a given class. It is implicit in the Guides that the entire range is available for use.
The guiding principal is that it should always be possible to make a logical and defensible argument in support of one’s decision.
Some aspects of this matter have been addressed in a previous newsletter of 7th September 2007 in relation to the grading of motor and sensory loss in peripheral nerve lesions. That newsletter was in response to a misunderstanding which had become prevalent at the time to the effect that only the upper end of the range could be utilised when grading peripheral nerve lesions: this is definitely not the case.
Often a very wide range of impairment may be available within a class. For example in table 69 of Chapter Three relating to lower extremity impairment due to peripheral vascular disease class 2 carries a range of 10% to 39% impairment of the lower extremity. In the grading of peripheral nerve lesions active movement against gravity with some resistance can result in a 1% to 25% motor deficit (table 12 of Chapter 3 or table 21 of Chapter 4). The impairment arising from Class 2 from a number of cardiac disorders is the range 10% to 29% of the WP (tables 5, 6, 8, 9, 10, 11, 12 of Chapter 6). There are many other examples through the Guides.
As the entire range is available for use, some patients will fall at the extreme lower end of the range, some at the upper end of the range and some at every point between. This fact is of some assistance in determining where a particular patient’s impairment should fall. Perhaps the simplest method is to look at the descriptor of the Class below and the descriptor of the Class above. If the assessor believes, for example, that a patient would fall into Class 2 in a table in which there are four possible classes it would be prudent to look at the criteria not only for Class 2 but also for Class 1 and Class 3. If the impairment is barely more severe than Class 1 then an impairment at the lower end of the range of Class 2 would seem appropriate. By contrast if the impairment is such that it almost achieves the criteria for Class 3 then an impairment towards the upper end of Class 2 would seem appropriate.
An example in which the issues are fairly well defined and quantifiable relates to the grading of muscle function. Grade 4 power is defined as active movement against gravity with some resistance. Clearly this represents a very wide range from minimally reduced power to power which is barely better than against gravity only. It is not difficult to indicate where in this range a particular muscle’s power may lie and indeed this is a routine part of physical examination. A muscle in which there is barely perceptible weakness will produce a rating at the extreme lower end of the range whereas a muscle that is barely better than grade 3 will attract an impairment at the top end of the range.
The descriptors in some other tables are of course less easy to quantify but the same principles apply.
Tables may refer to the intensity and frequency of symptoms. Some guidance as to the intended meanings of the words minimal, slight, moderate, marked, intermittent, occasional, frequent and constant is given in the glossary (page 316 of the Guides).
It might be expected that the examples quoted in the Guides would assist the assessor in deciding on an impairment rating within a range. In some cases, the reasoning for choosing a particular figure is not provided explicitly, so these examples are less helpful than they might be. They do, however, provide some calibration. In some chapters, however, a comment does more directly address how a decision was reached (see the examples in section 10.5 on colonic, rectal and anal impairment and several in chapter 6 on the cardiovascular system) and these may provide the assessor with valuable assistance.
Particular care is required when tables in the guides contain the important words - AND - OR. Many tables in chapter 6 and chapter 10 are of this type. Obviously, if all clauses are connected by AND, all must be fulfilled for the impairment to fit into that category. If there is a mixture of ANDs and ORs, careful reading is required to select a category and then careful thought to allocate an impairment within a range.
For inexperienced examiners it is always of value to review the opinions of more experienced colleagues to see whether one’s own assessment is in line with the opinion of others. This does not mean that one should avoid having an independent opinion but it does mean that if one finds that one’s assessments are consistently higher or lower than those of experienced colleagues perhaps some adjustment in calibration is required.
In some circumstances an impairment may be assessed in two different ways and one would generally expect that the two methods would result in roughly the same impairment assessment. If there is a wide discrepancy between the two methods this should also raise the question as to whether the correct assessment has been made in tables in which there is a substantial discretionary element such as a choice of a value within a range.
In summary, it is always appropriate to continually self-calibrate either by cross checking with other sections in the Guides or comparing one’s own assessments with those of colleagues who have assessed similar cases.
When choosing a particular impairment within a range that is offered by the Guides one needs to be able to argue sensibly the reasons for one’s choice and to be able to say why one has chosen to allocate an impairment at the lower, middle or upper end of the range.
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