Resultados finales

Two ma thema t i c a l mode l s , the Bayes i a n probab i l i ty model and a mul ti pl e l i near regre s s i on equa ti o n , were u sed to e s t i ma te the ages o f b ru i s e s objec t i ve l y , us i ng scores from the sel ected h i s to pa thol o g i c a l fea tures l i s ted i n res ul ts . The Baye s i a n probab i l i ty model wa s chosen for i ts s i mpl i c i ty , fl exi bi l i ty a nd s u i ta b i l i ty fo r h i s to l ogi c a l d a ta , wherea s the mu l ti pl e l i near regres s i on equa ti on was tes ted because o f i ts wi des pread use and proven s uccess w i th b i o l o g i c a l data

(

N i e e t a l . ,

1975 ) .

I t i s a bas i c precept when u s i ng ma thema t i ca l model s for b i ol o g i ca l c l a s s i fi ca t i on th a t they fi r s t b e 1 deve l o ped 1 u s i ng d a ta from a

reference sampl e , then 1 te s ted ! o n new d a ta

(

Oyama and Tats uoka , 1 956 ; va n Woerkom a nd B radma n , 1 96 1 ; Anderson and Boyl e , 1968 ; Boyl e a nd Anderson , 1 963 ; Kn i l l -Jones et a l . , 1 973 ; Sher , 1980 ) . I t i s

i mpos s i bl e to eva l uate the performa nce o f a modei rea l i s ti ca l l y wi tho u t

s o do i n g , a nd not to do so may res ul t i n overe s t i ma ti ng i ts perfo rmance by a s much a�

2m�

(

H i rschfe l d et a l . , 1974 ) . No nethel e s s , a model may be te s ted bac k o n i ts e l f provi ded the a i m i s to a s s e s s i ts po ten ti a l , a s o ppo s ed to i ts actua l , performa nce (Rogers et aZ. ' 1979 ) .

Ava i l ab l e d a ta were therefore d i v i ded i nto two groups : a reference sampl e fo r devel opi n g the mode l s a nd a s s es s i ng the i r po ten ti a l

perfo rma nce s , and a tes t i ng samp l e for a s s es s i ng the real worth o f the bes t model . The reference sampl e cons i s ted o f d a ta from one t i s s u e s ec t i o n sel ec ted a t ra ndom from e a c h of 20 b ru i ses p e r age c a te go ry , i . e . 120 ti s s ue s ec t i o ns . The rema i n i ng d a ta fo rmed the tes t sampl e . Da ta from mu sc l e a nd ad i po s e ti s s ue we re cons i dered separa te l y bec a u s e b o t h ti s sues a re not a l ways affec ted i n pra c ti ce , and comb i ni n g d a ta wou l d e l i mi nate these bru i ses from cons i dera ti on .

MASSEY UNIVERSITY LIBRARY

1 . Sel ec ti o n o f fea tu res

The h i s to pa tho l o g i c a l fea tures con s i dered for use when objecti vel y a ge i ng b ru i s e s ( F i gure

2 . 2 )

were those conventi o na l l y used to a ge wounds s ubjec t i ve l y ( Rae ka l l i o , 1977 ) . The i r scori ng on a sca l e o f

1 - 5 wa s neces s a r i l y i mprec i se , but the a p pl i ca t i o n o f Bayes ' equa ti on to s uc h data i s non-co ntrovers i a l ( Co l quhoun , 1 9 7 1 ) . As far a s

pos s i bl e the scori ng wa s u n b i a s ed , a nd t o th i s end bru i s e s were scored wi thout know l ed ge o f the i r a ges . Onl y macropha ge/ neutro ph i l ra t i o s were objec ti v e mea s urements , hav i ng been c a l c u l a ted from cel l counts . Ofte n , when q ua nt i ta t i ve l y scori ng h i s to l o g i ca l c ha nges , a gri d pa ttern sys tem i s a d o p ted to e n s ure that t i s s ue s ec t i o n s a re s tud i ed o n a

random b a s i s ( Bas sett e t a l . , 1 97 7 ) . Though d e s i rab 1 e , th i s a p proach wo ul d have been u n s a t i s fa c tory for brui s e s beca u s e the t i s s ue reac t i o n s were freque n t l y m i l d a nd confi ned t o sma l l area s w i thi ri t i s s ue s ec t i ons . Scor i n g wa s t herefore ba sed o n a n eva l ua t i on o f the enti re sec t i o n s . Score s were a s s i gned accord i ng to the de gree rather than the extent o f cha nge , e . g . scores for l eucocytes depended o n the dens i ty o f the ce l l u l ar exud a te rather than o n overa l l numbers o f cel l s . The extent o f d ama ge wa s a s s umed to refl ect pr i ma r i l y the s ever i ty o f i nj ury ra ther than i ts durati o n , though i t wa s real i sed that the earl y s tages of reac t i ve c ha nge are s e l f pro pa ga t i ng ( Rya n , 1977 ) a nd tha t for mus c l e i n par t i c ul ar , i schaem i c damage may become s uperi mpos ed o n tha t d i re c t l y due to the i n i ti a l i ns u l t ( Ho p k i nson a nd Wa tts , 1963 ) .

H i s to pa thol o g i c a l fea tures w i th scores s i g n i fi c a n t l y a ffec ted by the severi ty of i nj ury were eventua l l y i denti fi ed s ta t i s t i ca l l y by

control l i ng for sever i ty o f i njury i n c h i -square tes ts .

Bru i s e s had to b e re-a ggregated from fourteen to onl y s i x a ge c a te go r i e s ( i . e . 1 -8 , 1 2 - 20 , 24-36 , 48 , 60 a nd 7 2 hours ) s i nc e i t became o bv i o u s tha t they coul d not be a ged more a ccurate l y than t h i s . At the s ame t i me numbers o f bru i ses were i ncre a s ed s o tha t for musc l e a nd a d i p o s e t i s s ue con s i dered s e pa ra te l y there were d a ta from a t l ea s t 2 0 b r u i s e s per a ge c a te gory . Extra data acqui red wh i l s t perfec t i ng exp e r i me n ta l tech n i ques or from enzyme s tud i es were a l so i nc l uded i n the d a ta b a s e s i nce equa l i ty of numbers was not a prerequ i s i te for the method s of a na l ys i s eventua l l y used .

H i s to patho l o g i c a l fea tures were s e l ec ted accord i ng to the degree a nd va l i d i ty o f a s soc i a t i ons between the i r s cores a nd bru i s e ages . The sel ecti on proces s wa s e ffected by carryi ng out two sets of c h i - square a na l yses on data from ti s s ues w i th h i s to l o g i ca l evi dence o f h aemorrh a ge . T i s s ues w i tho ut haemorrhage were exc l uded from a n a l ys i s because

haemorrhage wa s con s i dered the fundame n ta l cri teri on of a bru i se .

When fea tures of pote nti a l use for e s t i ma t i n g bru i se ages were s e l ec ted , a l l val i d data were u sed to cons truct conti ngency tab l es re l a t i n g scores and bru i se ages . Al l data had to be u sed , wi thout regard to pos s i bl e b i a s from mul ti pl e sampl i n g , i n o rder to ful fi l the c h i - s quare a na l ys i s req u i reme n t tha t not more than 20% o f ta b l e c e l l s shou l d conta i n l e s s tha n fi ve d a ta u n i ts each

(

N i e e t a l . , 1975 ) . Even s o , i t wa s nec e s s a ry to comb i ne score categori es 2 - 5 for haemo s i de r i n a n d c a tegori es 4 and 5 for the o ther va r i a bl es . The s i gn i fi cance l ev e l s of c h i - squa re tests performed o n those va r i a b l es no t a l ready exc l uded because o f

i n s u ffi c i e n t data a re s hown i n Tab l e 2 . 4 . Scores for haemorrha ge and t i s s ue d i srupti o n were i nc l uded a s con trol s s i nce they were expected n o t t o be a s soc i a ted wi th age . T h e s i gn i fi ca nce l evel s ca l c u l a ted for haemorrha ge were of parti c u l a r i ntere s t beca u s e both the magn i tude and pos s i b l y the t i me-course of a t i s s ue rea c t i o n may be a ffec ted by the s everi ty of i nj ury

(

Stee l e a nd Wi l he l m , 1970 ) , a nd scores for haemorrh a ge were pres umed to refl ect t h i s fac tor . Al so , extrava sa ted b l ood c a n

i ts e l f i nduce a t i s s ue rea c t i o n i nd i s t i n g u i s h a b l e from tha t i n bru i s e s . Th i s had been s hown by a sma l l exper i ment

(

res ul ts not recorded

)

whereby a u to l ogous b l ood had been i nj ec ted i n to l ambs a nd t i s s u e s exami ned 16 , 48 , 1 20 a nd 1 4 4 hours l a ter . I t had to be a s s umed

therefore , tha t haemorrhage woul d i tsel f acco u n t for part of the t i s s u e rea c t i o n i n bru i se s . Fo r thi s rea s o n i t wa s d i s turb i ng to fi nd a

s i g n i fi c a n t a s soc i at i on be tween age and scores for the haemorrhage i n mu s c l e , s i nce i t ra i sed the pos s i b i l i ty tha t the s i gni f i ca n t a s soc i a ­ t i o n s between a ge a nd the rema i n i ng mus c l e pa rame ters were s puri o u s : mere l y refl ec t i ng the rel a t i ons h i p between mu s c l e haemorrhage a n d age . Three t h i ngs had to be cons i dered i n eva l ua t i n g thi s po s s i b i l i ty :

( i ) Wi th l a rge sampl es , s ta t i s t i c a l s i g n i fi cance does not neces s a r i l y i mp l y a s ub s ta n t i ve rel a t i o n s h i p ( F i nch , 1 978 ) ;

( i i ) The i n terpreta t i on of s ta t i s ti ca l res u l ts mu s t a l ways be w i th reference to the k nowl edge o f the i nves t i ga tor , i . e . s ta ti s t i ca l s i gn i fi cance s uggests but does not d i c ta te a conc l u s i on

( Col q uhoun , 1971 ) ;

( i i i ) There was no rea son to a s s ume a rea l rel a t i ons h i p between mu s c l e haemorrha ge a n d age i n the absence o f a s i gni fi c a n t paral l el rel a t i on s h i p betwee n haemorrha ge i n a d i pose ti s s ue and age

( P<0 . 2 1 ) .

Neverthe l e s s , i t wa s cons i dered necessary to cons truct a s econd s e t of conti nge ncy ta bl e s re l a t i n g scores to bru i se a ge s , th i s t i me contro l l i n g fo r the d i rect e ffects o f haemorrha ge ( Ta b l es 2. 5 a nd

2 . 6 ) .

I n th i s way i t wa s s hown tha t except for musc l e and fa t necros i s , the rel a ti on s h i ps between bru i s e a ges and s cores for the fea tures i n Tab l e 2 . 4 were

va l i d d e s p i te the co nfou n d i ng i nfl ue nce o f haemo rrhage .

2 . the Bayes i a n model

The Baye s i an proba b i l -i ty model wa s deve l o pe d by ca l c ul a t i ng the frequenc i es w i th wh i ch scores for fi bropl a s i a , e ndothe l i a l swel l i n g , haemo s i deri n a nd e i ther the ma crophage a nd neu troph i l exudates or mac ro phage/neutroph i l ra t i o s occurred i n the reference sampl e . The s e frequenc i es , a nd Bayes 1 equa t i on , were then u sed t o tes t the mod e l bac k o n i tsel f i n order t o emp i ri ca l l y ta. i l or i t t o i ts bes t

performa nce , i . e . s e l ect the b e s t comb i na t i on o f h i s topatho l og i ca l

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