hemiplegia?
The idea of a valid and reliable qualitative scale is not
new to physiotherapy and medicine. The Medical Research Council scale of muscle power (MRC, 1943) demonstrates objectivity and standardisation (Figure 14). Each item classifies muscle power in one of two categories ("at this grade" and "not at this grade"); and the itens form a cumulative scale which
describes muscle power with increasing force by each successive item or grade passed. It is an example of a perfect ordinal
i
scale: no person who can pass 5 cannot also pass 4, 3, 2 and 1; and no person who fails 4 can pass five. The same transitional relationships hold true for all items«, Consequently, the scale will predict the patient's performance of higher and lower ranked items from knowledge of one item which is passed or
failed. For example, if a patient cannot pass grade 3, it will be correctly predicted that he cannot pass grades 4 and 5. Alternatively, if he can pass grade 3, it will be correctly predicted that he can also pass grades 1 and 2.
The MRC scale has also been shown to possess the ability to predict a patient’s future status in special circumstances. Huckstep (1964) suggested a ’’rough but useful guide” to
estimation of the final grade of power which would be recovered by individual muscles affected by poliomyelitiso The author of this thesis used it at a children’s polio clinic in Kenya and found it to be empirically valid. However, recovery from polio is not equatable with recovery from hemiplegia due to CVA
because polio affects the motor fibres of the peripheral nervous s^dtem directly. In polio, recovery m a y be due to regeneration of nerve fibres, which is well documented (Seddon, 1954), and to hypertrophy of innervated muscle fibres. The Mr c scale of muscle power records recovery of power in isolated muscles, rather than recovery of co-ordinated activity of
muscles in patterns of movement. The scale is used here to illustrate the argument that a valid qualitative yardstick to measure resolution of impairment can be standardised, can have predictive validity and can discriminate between different levels of recoveryo
The first task in the development of a physiotherapeutic assessment of hemiplegia is seen as the development of an ordinal and cumulative scale from a set of qualitative items which describe resolution of hemiplegiao The reliability of the items will depend on the formulation of each one so that competent assessors will agree which performances belong in the ’’acceptable/pass" category and which do not (Schultz, 1958).
2.6.3 Selection of an appropriate method of scaling
The texts of Torgerson (1958) and Maranell (1974) discuss methods of achieving order with qualitative data which have been developed by behavioural scientists. There are no un equivocal criteria for classification of these scales in the way nominal, ordinal interval and ratio scales are distinguished. Therefore, in order to apply a scale to assessment of hemi plegia, it is necessary to select a method of scaling in which the underlying premises are theoretically appropriate both to the function of clinical assessment and to the nature of recovery from hemiplegiao v
A logical choice can be made by deduction according to three propositions:
1. The relationship of the subject to the item. 2. The nature of the subject’s response.
3. The correspondence of the scale to the available data.
1. The relationship of the subject to the item: The first choice is between response methods and judgment methods.
Response methods relate the item to the subject. It seems obvious and bathetic to say that an item of assessment would assess the patient. However, judgment methods, such as Thurstone’s Judgement Scaling Model (Thurstone and Chave, 1929) require the subject to evaluate the item with respect to some attribute it possesses. Therefore, response methods are more appropriate to clinical assessmento
2. The nature of the subject’s response; The second choice is between categorical responses and comparative responseso
A categorical response requires the subject to endorse the item and to be characterised in some way by it. Consequently,
subjects will be classed in mutually exclusive categories of the item. The alternative comparative response, such as that
required by the Coombes Model for Comparative Response (Coombes, 1954), requires the subject to prefer one item over another.
Therefore, a method for categorical responses is appropriate because a hemiplegic patient would be able or unable to perform an item. Consequently, he would both endorse its position on a scale of "least recovered" to "most recovered" items and be characterised as passing or failing the item.
3• The correspondence of the scale to the available data: The final choice is between a deterministic model and a latent distance model.
A deterministic model is stated in terms of an ideal which is not expected to hold true exactly with real data but to provide a very close approximation to them. Response is determined by the individual relationship of each subject and each item to the variable underlying the scale. Alternatively, in
Lazarsfeld’s Latent Distance Model (Lazarsfeld and Barton, 1951) the parameters associated with the subject and the item determine the probability of the subject responding in a given way.
Therefore, a deterministic method which states an ideal model is appropriate to physiotherapeutic assessment of hemiplegia. As required, each patient and each item of assessment would be related to resolution of hemiplegia. It would not be necessary for the progress of every patient to conform to the order of the items in every respect as long as the order
approximates very closely to the sequence of recovery displayed by hemiplegic patients as a whole. Therefore, it would
accommodate deviations due to various as yet undefined independent variables. However, this method also presents three central problems:
A. Deciding whether recovery from hemiplegia or