Prueba de hipótesis para la trabajabilidad del concreto fresco

4F.1 SUMMARY

(1) The statistical model predicting the level of independ­ ence a c h i e v e d by stroke p a t i e n t s w i t h visu a l n e g l e c t is based on a representative sample of patients, makes clini­ cal sense and is accurate in predicting independence and moderate/severe dependence.

(2) The a c c u r a c y of the model m a y h a v e b een a f f e c t e d by other f a ctors not taken into account, such as the p r e ­ st r o k e l e v e l of i n d e p e n d e n c e a n d l ack of s t a n d a r d i z e d treatment.

(3) The r e g r e s s i o n equations g e n e r a t e d by the m o d e l are relatively simple, requiring assessment of only two clini­ cal variables using standardized clinical methods.

(4) A l t h o u g h the r e g r e s s i o n e q u a t i o n s m a y be limited in pr e d i c t i n g out c o m e for i ndividual patients, t hey m a y be u s e f u l in s e l e c t i n g c o m p a r a b l e g r o u p s of p a t i e n t s for trials of treatment of visual neglect.

4F.2 The statistical model

The statistical model resulting from the present study is

based on a representative sample of stroke patients p r e ­

s enting to a d i s t r i c t g eneral hospital. The s i g n i f i c a n t predictive factors make clinical sense. Power loss (Allen 1984; M a r q u a r d s e n 1969; Wad e et al 1983; W a d e + H e w e r 1987; Fullerton et al 1988) has previously been identified

as a prognostic factor as have both the presence (Adams

and Hurvitz 1962; Feigenson et al 1975; Kinsella and Ford 1980; Denes et al 1982) and the severity (Fullerton et al 1988) of visual neglect. Motor skills are important in self care, and the difficulties of using a hemiparetic limb in that side of space, or of compensating by using the n o n ­ weakened limb in that side of space, would be exacerbated by visual neglect.

Although A N OVA did not show that age was significant on its own, it was significant when taken into account with the other v a r i a b l e s in logistic r e g r e s s i o n . T h e a d v e r s e effect of age has been noted in other studies (Marquardsen 1969; Wade et al 1983; ade + Hewer 1987; Allen 1984; Henley et al 1985). This may reflect loss of neurological reserve after injury to the brain but may also reflect lower expec­ tations of physicians and therapists for older patients and thus less sustained attempts at active rehabilitation.

The predictive accuracy of the model was high for inde­ pendence (sensitivity 84%, specificity 90% at 3 months) and for moderate/severe dependence (sensitivity 89%, specifici­ ty 80%). Prediction of mild dependence was less accurate. The accuracy of prediction in this and other (Fullerton et al 1988; A l l e n 1984; H e n l e y et al 1985; P r e s c o t t et al

1982) p r o g n o s t i c studies of stro k e m a y be l i m i t e d by several factors. First, neither remedial therapy nor medi­ cal treatment is likely to have been standardized in the sample of patients examined; although nearly all patients received occupational as well as physiotherapy, none r e ­ ceived specialized therapy for visual neglect and m a n y of t h o s e w h o r e a c h e d a B a r t h e l s c o r e of 20 r e c e i v e d less

therapy than those with worse outcomes. Second, the p r e ­

stro k e level of indep e n d e n c e m a y not have b e e n c l e a r l y established. This may explain why, for example, a signifi­ cant proportion of patients predicted to be independent in fact had a Barthel score of 18-19, owing to pre-existing inability to bath or to climb stairs; future studies should p r o b a b l y take this into account. Third, factors s u c h as motivation, known to affect outcome (Henley et al 1985) may not be measured.

The predictive equations derived from the model are rela­ tively simple, requiring assessment of only two clinical variables, visual neg l e c t and power. The a s s e s s m e n t of power is closely related to the standard clinical method, and the VNRI is based on the Behavioural Inattention Test

(Wilson et al 1987), which is being increasingly use d by occupational therapists. The neccessary mathematics can be p erformed by a basic pocket calculator. The equation is a l i t t l e s i m p l e r t h a n t h o s e p r o d u c e d b y F u l l e r t o n et al (1988), which contain 6 variables, some of which have to be weighted (Hodkinson's Mental Test Score) and some of which (eg leg power, arm function) are not standardized measures.

The current study contirmed the findings of Fullerton et al that the initial severity of visual neglect was a p r e ­ d i c t o r of outcome, and t h a t b e i n g " u n a s s e s s a b l e " for

n e g l e c t w a s a g o o d p r e d i c t o r of d e a t h (Se c t i o n 2.7F). However, the study avoided the possibility of exaggerating the a s s o c i a t i o n of n eglect w i t h a p oor outcome, b y not allocating the mean VNRI score to the "unassessables" and by not including death as an outcome. Moreover, use of a l a r g e r b a t t e r y to a s s e s s v i s u a l n e g l e c t i n c r e a s e d t h e d e t e c t i o n of pat i e n t s w i t h t his deficit. W h e n d e a t h was i ncluded as an additi o n a l outcome, logistic r e g r e s s i o n found that the same factors (power loss, neglect and age) were significant. 88% of independent, 37% of mildly depend­ ent and 88% of moderate/severely dependent outcomes were correctly predicted, but only 10% of deaths pro b a b l y b e ­ cause their number was so small. The separation of "depend­ ent" patients into two groups that reflected the practical difficulties of arranging a discharge, facilitates identi­ fication of a group in particular need of attention. Had a larger number of patients been recruited, this mig h t have a ll o w e d s e p a r a t i o n of the " m o d e r a t e / s e v e r e " d e p e n d e n c y outcome group into its two constituent groups, which might have enhanced the usefulness of the study. Consideration should be given by future prognostic studies to prediction of functional recovery from the clinical features p resent a t 3 w e e k s r a t h e r t h a n at 3 d a y s , as at t h i s t i m e , the majority of deaths have occurred (Wade + Hewer 1985a; A h o et al 1980) , the r a pid p h a s e of early r e c o v e r y has ended (Wade et al 1985a) and any cerebral oedema will have r e s o l v e d (Spatz 1939; Skr i v e r + O l s e n 1981), l e a v i n g a "core" neurological lesion.

Lincoln et al (1990) have recently pointed out the limita­ tions of prognostic studies in predicting exact outcome for

i n d i v i d u a l p a t i e n t s , but s t r e s s e d t h e i r u s e f u l n e s s in targetting a group of patients in need of special interven­ tion. The r e g r e s s i o n equations g e n e r a t e d by the cur r e n t study could be used in such a manner to select patients for trials of treatment of visual neglect.

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