AMA4 Induced Chaos, comparing the NZ and NSW revisions of the Mental and Behavioral Disorders chapter

April 20, 2013

Illustrating the chaos that has resulted from the inability of the authors of the AMA Guides 3-5 to provide a method of assessment. New Zealand has modified AMA  4 chapter 14 Mental and Behavioural to produce the ACC Handbook.See also Bizarro World II.

The Motor Accident Authority in New South Wales published the Psychiatric Impairment Rating Scale also modifying chapter 14 AMA4. It is salutary to compare the two versions.


The ACC User Handbook to the AMA “Guides to the Evaluation of Permanent Impairment” 4th Edition

Using the same table in chapter 14 AMA 4 the New Zealand version is compared with the PIRS

ACC Handbook                         PIRS

class 1- 0-9%                               0-3%

class 2-10-35%                           4-10%

class 3-36-60%                         11-30%

class 4-61-79%                          31-59%

class 5-80-100%                         >60%

In the NZ system the figures taken from the four categories are not added, averaged or combined. The figures are to assist the assessor, in conjunction with clinical judgement, to arrive at a whole-person impairment rating based on the claimant’s current level of functioning, and expressed as a single percentage.

The Guidelines state:

  • An EXTREME rating in one category implies that the individual is highly unlikely to perform satisfactorily in any of the categories.
  • A MARKED rating in two categories implies that the individual is unlikely to be able to perform any complex task without support or assistance.
  • A MODERATE rating in four categories should be considered to be moderate overall. (That is, they aren’t additive.)

The final whole -person impairment rating is not expected to be:

  • Less than the lowest of the figures selected to represent impairment in the four categories of function; or
  • Higher than the highest of the figures.

The PIRS determines the  number for each category (the four categories have been broken up into six categories). The middle number that is the median number is determined and that is the final class. The numbers for each category are then added together. The sum of those numbers is used with a table correlating the median class with the total number of producing the final percentage impairment. Ironically a claimant may score in class 2 for each category leading to a median class 2 and a sum of 12 but the final percentage impairment is 6%!

The following examples illustrate the differences

Concentration, Persistence, and Pace

NZ ACC Handbook Class 2 Mild – 10–35%

Independent, but in some areas functioning is not particularly effective.

Impairment levels compatible with some (but not all) useful functioning.

Examples: ̇Can undertake basic training. But may have difficulty concentrating on complicated instructions.

̇Can focus intellectually on demanding tasks, but possibly only for a limited time.

̇Usually employed, but may have erratic work history marked with periods of unemployment.

̇May need some assistance with such things as decision making and finances.


Concentration, Persistence and Pace

Class 2 –  4-10% Mild impairment: Can undertake a basic retraining course, or a standard  course at a slower pace. Can focus on intellectually demanding tasks for periods of up to thirty minutes, e.g then feels fatigued or develops headache


These absurdities are what led to a total rewrite of the chapter . We were all hopeful but something meaningful would urge,alas our hopes were dashed . The American Medical Association Guide to the Evaluation of Permanent Impairment 6th edition chapter on Mental and Behavioural Impairment (AMA6) has ditched the previous non-method and has substituted a dog’s breakfast. The method developed involves use of the Global Assessment of Function scale in the DSM IV, the Brief Psychiatric Rating Scale BPRS and a modified version of the PIRS. One is expected to combine the results from these different methods producing a final number. The GAF is so vague as to be almost useless, the BPRS is used to assess whether treatment has made any change for people with serious mental illness with an initial measurement and then a later measurement. Although it has been validated and is reliable, not in this context. I have already commented on my concerns about the PIRS.

This process is very time-consuming and is not, to say the least, an advance.


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