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3. BACKGROUND TO THE METHODOLOGY
3.1 Case Study Methodology: The literature on case studies as an experimental technique and the rationale for the choice of
format for this study are examined.
A case study format with multiple subject baselines was chosen to examine the research question of whether therapy that targets the respiratory system in isolation will improve the speech of patients with MS. This section will examine the issues in the choice of the appropriate case study methodology.
In the largest long term care facility for the severely disabled in Britain 120 of the 350 beds are occupied by MS patients, a seemingly large pool of available subjects. As noted previously between 19% and 40% of patients with MS develop a dysarthria (Beukelman et al. 1985, Darley et al. 1972). Thus, hypothetically, one
would expect the pool of patients with dysarthria and MS available for research to be about 35.
For the proposed therapy it was necessary that the dysarthria be in the middle stages of severity. Subjects who had abnormalities in their speech which had not yet affected their intelligibility could not participate since it was specifically speech intelligibility that was being measured as a global, objective and accessible indicator of therapy effectiveness (see Section 3.2.2). Similarly if a subject was anarthric or aphonic, and therefore at the opposite end of the continuum to the mildly dysarthric, intelligibility tests would not be an appropriate tool to measure any effectiveness of respiratory training in individuals with no speech or voice. Also individuals who were severely neurologically involved would probably not have the motor control to participate in the therapy. It was decided that appropriate subjects for this study would have speech that was less than 80% intelligible so that there was room to show an improvement in their intelligibility as a result of therapy should it occur, and yet were not so impaired that speech was effectively unintelligible. It is not suggested that respiratory therapy may not be of use to the mild and severely dysarthric. Smeltzer (1988) notes that respiratory symptoms occur early in MS, whether for reasons of neurological involvement or lack of use. Thus it is reasonable to suppose
that respiratory training might be beneficial to these individuals. However a
completely different methodology and assessment tool would need to be developed to measure the benefit to these individuals. The same argument is true at the other end of the scale. Respiratory muscle training may improve the respiratory capacity of severely neurologically involved individuals if they were capable of participating but the potential benefits would need to be clearly defined and appropriate measures specified. Thus, for this study, the appropriate subjects had a dysarthria that rendered
their speech less than 80% intelligible but still capable of being measured with the chosen intelligibility measure: the Assessment of the Intelligibility of Dysarthric
Speech by Yorkston and Beukelman (1979). The files of the speech therapy
department at this institution were examined and the speech therapists’
recommendations taken for patients who fulfilled these criteria. This left eight
subjects at the institution with a dysarthria in this range from the original 120
moderately to severely disabled MS patients. All eight of these subjects were
interviewed and six participated in the initial assessment. O f the eight, one subject did not wish to take part, one was not available during the research time frame and one was about to have significant changes made in his treatment and pattern of care which might mask therapy changes. Thus five subjects were available for the study.
This highlights what is a major difficulty in organising efficacy studies for specific, individualised therapies. Speech therapy involves the assessment of specific difficulties in the components of the speech process. Group studies are inappropriate as the chances of finding sufficient individuals with exactly the same grouping of motor or, as relevant, cognitive or linguistic disabilities is extremely difficult. Even if such individuals are identified the logistics of participation in a study are often a nightmare:
“Many drop out, they move away, withdraw from the trial, get ill, die or even recover. Of those that continue in the study many do not get nearly as much treatment as intended” (Howard 1986, pp.94).
Even in this case where a large number of patients with multiple sclerosis in a similar stage are resident in the same setting, since the given therapy technique and the measurement tool focuses on a specific symptom or ability the available subjects are further divided. While the therapy itself may be very relevant and helpful to individuals with that configuration of symptoms there is no point in a research
methodology that addresses individuals without these symptoms to make up group
numbers. The logistics of getting specific symptom sufferers in a group study
methodology would make efficacy studies of these therapies impossible. Mathews et al. (1985) updating McAlpine’s renowned work on multiple sclerosis research make the following comments:
“No critical evaluation of the merits of physiotherapy in
multiple sclerosis appears to have been published. This is
scarcely surprising as the difficulties of assessing even a standardised method of treatment are sufficiently daunting and it would perhaps be impossible to devise a method of
examining the results of necessarily individualised
physiotherapy.” (pp.268)
While these comments apply equally to speech therapy the situation is not as bleak as McAlpine paints. Single case study methodology is entirely appropriate to addressing the efficacy of highly individualised therapy regimes. Howard (1986) in his persuasive argument for the appropriate use of single case studies rather than between groups research designs for studies of the efficacy of aphasia therapy makes exactly this point. His analysis states that between group studies addressing the efficacy of speech therapy for aphasia have involved large groups studies where neither the particular aphasie symptoms of the subjects nor the treatment regime given to them was detailed. That most of these trials found no difference between treated and untreated groups was not then surprising. The same observations are also relevant to efficacy studies in dysarthria and are subject to the same methodological demands. First, the treatment must be specified clearly so that results are capable of replication and the body of knowledge available to practising clinicians develops. Second, the individual characteristics of the subject who received the treatment must be specified so that it is possible to judge the appropriateness of a specific subject to the therapy regime advocated. When these demands are met it is possible to show that therapy
changed the performance of an individual on a given task. With replication it is possible to draw firmer conclusions about the wider population to which the therapy applies. Case studies provide methodological concerns of their own which must be addressed in the analysis of results whether by visual inspection or by appropriate statistical methods (Pring 1986; Kazdin 1982). Data analysis methods appropriate to this study are discussed subsequently (see Section 5.1).
Single case methodology in dysarthria research has received far less attention than the question of appropriate methodology for aphasia efficacy studies. Ludlow (1991) discusses the place of single subject designs in the development of new treatment in dysarthria and emphasises the need to have the repeat measure suited to the specific purpose or deficient being investigated. Keatley and Wirz (1994) report the result of a reversal and withdrawal design on a dystonie patient of long standing. LeDorze et al. (1992) report a single subject multiple baseline across behaviours experimental design of a subject with Parkinson’s disease. Both investigations detail specific treatment regimes suited to particular speech behaviours. Thus replication of methods and subjects is possible which is the only way that the single case methodology can legitimately be used to generalise about the appropriateness and efficacy of treatment. This study chose a multiple baseline across subjects for exactly this reason. The clinical impression of generally successful speech therapy with MS patients (see Section 1.6) needs to be examined within the general context of the question of respiratory insufficiency being a reversible component of the dysarthria. A between group study was impractical and inappropriate. In this study a very specific type of therapy is proposed which can be specifically detailed. As several subjects were available at the same time a multiple baseline across subjects was chosen since, as Pring (1986) comments, this is the preferred single case methodology
as it has a “built in” replication component (pp. 107). A multiple baseline methodology involving several behaviours is inappropriate since it is often difficult to independently demonstrate the effects of therapy on different levels of speech functioning and at different times. Indeed when therapy is targeting respiration exactly the opposite is expected. It is reasonable to hypothesise that the improved respiration patterns and capabilities would cause improved airflow which will effect efficient laryngeal valving and phonation which may then cause articulation to appear crisper and resonance better. Respiration is the base that underlies speech but it is not in itself an isolated, measurable component during the speech act: to separate one
effect from the other is impossible. Instead in this methodology by specifying
treatment in detail and allowing a generalised measure of improvement, speech intelligibility, there is no attempt to tease out the effect of the specific therapy upon a specific behaviour. Olgiati et al. (1988) showed respiratory function improved when respiratory skills were trained: the question here is whether speech function improves with respiratory training. This question necessitates a general repeat measure but a highly specific therapy regime using the several appropriate subjects available.