THE W.H.O. conference on medical statistics, heldin London last week,l differed from many other inter-national gatherings of this sort by arriving at a firmand constructive conclusion : the delegates acclaimedthe concept of national committees, composed ofinterested people from government and medicine,linked by a W.H.O. central unit and refreshed byregular international conferences. The intention isthat these should act as a statistical conscience,stimulating and training people to do fresh work,getting rid of useless routine tabulations, and publi-cising the value of statistical research. The means tothis end were the main topic of discussion.The conference crystallised the notion that sampling
procedures are often cheaper, quicker, and better thanapparently complete collections of vital-statisticaldata. In the technically advanced countries, whereregistration of births and deaths is essential to thesmooth working of systems of social security, this iseffected completely and reliably. In no country,however, is the cause of death always recorded
accurately-the registered causes of death from morethan one disorder in older people are particularly opento question-and in some countries the certifyingphysician may be influenced by the legal and psycho-logical consequences of certifying certain causes. This
difficulty can be overcome by necropsy or other specialinquiry in a small but representative sample. Then
1. See Lancet, Oct. 17, 1953, p. 818.
defined cause, the only possible way to learn moreis to investigate a representative sample and to
generalise from the results thus obtained.Without trained staff, all this would be out of the
question, and the conference made parallel recom-mendations on training. The United Nations centralstatistical organisation is producing instructionmanuals ; and the exchange between different countriesof coding details and other training material shouldensure accuracy and uniformity in classification.Furthermore, the epidemiological and statisticalsection of W.H.O. is being encouraged to attune
training methods to the public-health requirements ofmember countries. These and other measures, such as
special courses and fellowships, will help to meet theneed for lay " health statisticians," and for medicalspecialists in preventive medicine to interpret anduse the results obtained. The main problem nowrests with our own profession. Unless the generalpractitioner is convinced that certification has a
clearly useful object, he is not going to give it theconscientious attention it demands : he must see thatthe data he provides are used quickly and effectivelyby other medical men-locally, nationally, and inter-nationally. It is his interest that the nationalcommittees must strive to seize and sustain.
1 King, J. T. Arch. Intern. Med. 1926, 38, 69.2. Lewis, T. Heart, 1933, 16, 205.3. Evans, W. Quart. J. Med. 1933, 2, 1.4. See Lancet, Sept. 19, 1953, p. 604.5. Brock, R. C., Graham, A. J. P. Guy’s Hosp. Rep. 1952, 101, 207.
Coarctation of the AortaANATOMISTS have recognised aortic coarctation for
two hundred years. Yet less than thirty years ago acardiologist declared that " the diagnosis is rarelymade during life " 1 ; and it was only after the publica-tion in 1933 of accounts by LEWIS 2 and EvANS 3 thatthis situation was changed. Coarctation of the aortais a very serious abnormality. A few patients with itreach old age ; but without surgical treatment manydie in infancy, and of those who reach the age of 17more than half die before the age of 34. The remark-able advances in vascular surgery 4 have, however,entirely changed the outlook.The cause of the defect is unknown ; but it has been
found in embryos and is probably a true error of
development, unconnected with the closure of theductus arteriosus. Its prevalence is difficult to assess ;but it must be lower than the necropsy figure of 1 in2000, and obviously it is higher than the 1 in 80,000estimated from mass-radiography examinations. A
useful distinction may be made between : (a) theso-called infantile type, where the defect is usuallysevere (sometimes amounting to atresia of the aorta)and is often accompanied by other congenital defectsin the cardiovascular system and elsewhere ; and(b) the adult type, where the narrowing is less severe.With this type there is commonly no other seriousabnormality ; but in 25% of cases there is a bicuspidaortic valve, and the prevalence of berry aneurysmsat the base of the brain is undoubtedly higher than theaverage. In some cases, too, the ductus arteriosusremains patent. In the adult type the constrictionvaries from -an annular stenosis to a narrowed segmentseveral centimetres long. The constriction is usuallyjust below the opening of the ductus, but may be at orabove this level, or occasionally in the lower dorsal 5
or abdominal aorta. With the stenosis there is oftenkinking and distortion of the proximal aorta ; this
may involve the left subclavian artery, which maybulge laterally and make the radiographic appearancemore confusing. The aorta on both sides of thestenosis may be dilated ; proximally the dilatation,sometimes aneurysmal, may be partly due to theassociated hypertension, but below the stenosis this
. cannot be so, and no entirely satisfactory explanationhas been found. It is known, however, that the vesselwalls near the coarctation may be defective and
lacking in elastic tissue, and this may be connectedwith a lack of the stimulus normally provided byarterial pulsation. The presence of a high resistance inso large an artery produces considerable changes in thecirculation. In patients who survive, the adjustmentis remarkably successful, and the blood-flow in thelower limbs is usually quite normal. The collateralcirculation which develops takes much of the totalflow ; but although this is normally very free it has ahigher resistance than the normal channels, and thedrop in pressure across these resistances is offset
by a rise in the proximal blood-pressure. This in turncalls for a compensatory mechanism to moderate theflow through the upper half of the body, and in factthe forearm flows are normal. The hypertension,however, usually contributes to the patient’s death,which may be due to cardiac failure, subarachnoidhaemorrhage, or rupture of the heart or aorta : but afew succumb to bacterial endarteritis, usually affectingthe aorta just below the coarctation.The diagnosis of coarctation, provided the condition
is kept in mind, is usually simple. The finding of ahigh blood-pressure, especially in a patient of good-or even superior-physique should lead to palpation ofthe femoral pulses, which are always diminished andoften absent. The femoral pulse, when present, is
delayed, compared with the radial pulse, mainlyowing to the slow rise in the pulse wave ; the veryslight lag occasioned by the longer collateral route isimperceptible. 2 This diminution of the pulse wave,however, does not mean that the blood-pressure inthe legs is very low.
Direct measurement from the femoral artery showsthat, though the pulse pressure is small, the meanpressure is lowered by no more than 10-15 mm. Hg andalways by much less than the reduction in systolic pres-sure, which may be 80-100 mm. Hg. This is because thepulse wave is heavily damped by the resistance of thecollateral vessels and the distensibility of the distalaorta. The position is analogous to that in patients witha collateral circulation around a thrombosis of a largeartery ; EDHOLM et al.6 have found that in the affectedlimb the flows and pressures are relatively normal.The drop in pulse-pressure may silence the Korotkoffsounds, thus making it impossible to take the blood-pressure by the auscultatory method and reinforcingthe mistaken impression that the leg pressures are verylow. Many other clinical signs of coarctation havebeen described, but though they may occasionallydraw attention to the condition they add little or
nothing to the certainty of the diagnosis. Perhaps themost valuable of these additional signs is the presenceof dilated collateral vessels over the back ; but theseare not always visible and are seldom definite in
patients under the age of 10 years. Occasionallymurmurs are audible ; but they are not usually a6. Edholm, O. G., Howarth, S., Sharpey-Schafer, E. P. Clin.
Sci. 1951, 10, 361.
prominent feature and are certainly of no diagnosticimportance.
Radiology plays little part in the diagnosis of
coarctation, since this can be so readily established byclinical examination, but occasionally notching of theribs may draw attention to the disorder. The notches,which are on the inferior margins of the ribs, are dueto the elongated and tortuous intercostal arteries asthey participate in the collateral circulation by bring-ing blood from the shoulder-girdle and chest wall backinto the aorta. (The first one or two ribs are notaffected since their intercostal arteries arise from thesubclavian artery-i.e., above the coarctation.) For
many years this appearance has been regarded as
pathognomonic of coarctation. It is not found, how.ever, in every case, and is seldom distinct in patientsunder 10-12 years of age. In a few cases notching hasbeen seen in congenital cyanotic heart-disease,’ and itmay also develop after a successful attempt to increasethe pulmonary circulation by establishing pleuraladhesions. 8 It is usually best seen in the middle ribsand is clearest about 2-3 inches lateral to the spine.It should not be sought along the necks of the ribs, asthese areas so often appear wavy. The heart shadowmay be rounded or globular but is not usually muchenlarged, and if left ventricular enlargement is pro-nounced aortic reflux should be suspected. The aorticknuckle may be absent ; but just as often there are toomany
" aortic knuckles," from shadows thrown by thekinked subclavian artery and by the dilatation of theaorta above and below the constriction. The site ofthe coarctation is not easily displayed by plain radio-graphy ; ; but it may sometimes be demonstrated inlateral or oblique tomograms, or by careful examina-tion with a barium swallow.9 Not infrequently theappearances are complicated by the presence of ananeurysm above or below the constriction, or arisingfrom the narrowed segment itself or from an inter.costal artery. Angiocardiography should always bedone before the patient is operated on, since this mayshow the length and calibre of the narrowed segmentand the disposition of the great vessels. Great cautionis needed in interpreting the filling-or non-filling-ofaneurysms, for the degree of filling is not always areliable indication of the flow.10 Adequate picturesmay occasionally be obtained by intravenous injection;but direct aortography 11 gives shadows of much
greater density and contrast, and this method shouldalways be used.
Coarctation was first corrected surgically byCRAFOORD 12 in 1944, when he resected the narrowedsegment and did an end-to-end anastomosis in a 12-year-old boy. Simple resection is still the operationof choice ; ; but in certain circumstances, as GROSS 13has pointed out, end-to-end anastomosis may be
impossible, and then grafting with a length of humanaorta may be the only way of bridging the gap. Manywill think, with BROCK, that no-one should start anoperation for coarctation unless he has a graft in hisbag-it will not always be used. The graft need notbe viable, as judged by tissue-culture it seems to act7. Batchelder, P., Williams, R. J. Radiology, 1948, 51, 829.8. Barrett N. R., Daley, R. Brit. med. J. 1949, i, 699.9. Bobbins, L. L., Wyman, S. M. New Engl. J. Med. 1953.
248, 747.10. Lancet, 1953, i, 1082.11. Jonsson, G., Broden, B., Karnell, J. Acta Radiol,, Stockh.,
suppl. 89.12. Crafoord, C. J. thorac. Surg. 1945, 14, 347.13. Gross, R. E. Ann. Surg. 1951, 134, 753.
merely as a scaffold into which new intimal andadventitial coats can grow. The best age for operationhas not yet been decided. On the one hand, it seemsthat grafts do not grow with the rest of the body, andshould therefore not be inserted until the patient isnearly full-grown and has a fully developed collateralcirculation ; while, on the other hand, degenerativechanges may develop in the aorta and elsewhere duringadolescence and thus increase the technical difficultiesof the operation.. Furthermore any unnecessary delayis undesirable since coarctation is a constant threat tolife. Up till now the supply of grafts has been verylimited and the surgeon has often had to wait untilone is available, but the results of recent experimentson sterilisation and preservation of grafts have beenmost encouraging,4 14 and it may be possible soon toestablish a graft bank. It is not yet known whethersuch theoretical risks as shrinkage of the graft or, con-versely, of aneurysm formation will be encountered inpractice ; but this uncertainty should not hinder workwhich has already provided brilliant short-term results.Delay may be fatal, and many surgeons can recallpatients who have died while their names were on thewaiting-list.
14. Hufnagel, C. A., Eastcott, H. H. G. Lancet, 1952, i, 531.15. Bull. World Hlth Org. 1953, 9, 423.
Vagaries of IntelligenceIT is widely believed that every child is served out
with a limited quantity of intelligence, which-like therest of him-can go on developing till it reaches thelimit of its capacity, but which cannot otherwise beexpanded. The mature intelligence is thus thought tobear a direct, possibly predictable, relation to theinitial ration issued by heredity, just as the size of aJapanese pith flower which has expanded in waterdepends on the original size of the bit of pith. This
practical and convenient assumption is backed by theintelligence quotient (l.Q.), which is taken to remainroughly stable throughout life. Many have criticisedthe reliability of tests for assessing the l.Q., and almostas many have thrown doubts on the underlyingassumption ; but these have had less publicity. Onanother page, Mr. A. D. B. CLARKE, PH.D., and Mrs.A. M. CLARKE, PH.D., bring fresh evidence that theassumption is untenable ; and a group of papersrecently published strongly support their contentionthat intelligence, far from being a fixed quantity, mayvary considerably during a lifetime.Mr. J. TIZARD, PH.D.,15 discussing criteria of mental
subnormality, deals first with weaknesses in our
methods of testing. A child’s performance in tests isby no means constant from one test to another ; so
when a group of children are tested and retested by astandard method, such as the Binet test, though theaverage I.Q. remains much the same, individual l.Q.smay vary considerably.Thus in a test with a test-retest correlation of 0-9 on
immediate retesting, and a standard deviation of 16points, one child out of every three who gained averagescores of 100 on the first test would, on being retested,score above 107 or below 93 because of " errors ofmeasurement " ; and one out of every ten children withaverage scores of 100 would score above 112 or below 88on the second test.
An I.Q. of less than 70 is very widely accepted asevidence of mental subnormality-sometimes on thebasis of a single test. It seems that one child in three
who scored 80 at a first test might, at a second test,fall into the subnormal group. Again, early revisionsof the Binet test were believed to have a standarddeviation of 12-13 points ; and an i.Q. of 70 pointsthus fell about 21/2 standard deviations below themean, and cut off 1% of the population. On somerecently devised tests, however, the standard deviationis nearly twice as much ; and an i.Q. of 70 falls justover one standard deviation below the mean, and socuts off 10% of the population. Another difficulty isthat the standard deviation sometimes varies forchildren of different ages.Thus the 1937 revision of the Stanford-Binet test has
standard deviations varying from 13 points at the age ofsix to 20 points at the age of twelve ; and an i.Q. of 74achieved by a six-year-old on this test is thus equivalentto an i.Q. of 60 achieved by a twelve-year-old.TIZARD also points out that even if scales for
measuring intelligence were absolutely reliable-in thesense that qualified observers would agree perfectlyabout each person’s standing on the scale-it wouldstill be impossible to predict infallibly the subsequentperformance of those tested ; for our present testsgive only one point on a curve of growth and develop-ment, and " the slope of the curve is not the same forall individuals." Many studies have been publishedabout this fluctuation in performance. He quotes thefindings of HONZIK, MACFARLANE, and ALLEN 16 thattests of two-year-olds predict performance at the ageof five to an extent little better than chance ; and
though prediction improves as the age of the childrises it is always hazardous.
In a given group of children the i.Q. changed, duringthe growing period of six to eighteen years, by as much as30 or more points for 9 % of the group, by 20 or morepoints for 33 %, and for 15 or more points for 60 % ;it changed less than 10 points for only 15 %. Thus forone out of every three children a, prediction made- at asix-year-old test would be wrong by 20 points at the ageof eighteen.As CLARKE and CLARKE say, " it is clear that in thegeneral population the concept of a rigidly constantI.Q. is contradicted by the facts ; I.Q. constancy overlong periods of time during the years’of mental growthis the exception rather than the rule." Some findingsreported by Dr. NANCY BAYLFY,17 from the Instituteof Child Welfare at the University of California, bearon this.
A study was made of a group of adults of superiorintelligence, who were tested by a " concept mastery "test designed by members of the Terman gifted studygroup at Stanford, and tested again twelve years later.Changes in scores between the two testings were com-pared on the basis of scores in the final test, sex, age-group, educational level, occupational status, andestimates of general " success " ; and some individualsin each of these classifications had improved their scoreover the first testing, among them the two oldest peoplein the group-who, moreover, scored higher in bothtests than the group averages.
Whatever may finally prove to be the predictiveaccuracy of intelligence tests for adults, those availablefor testing young infants, even when they are carriedout by an experienced and informed tester, certainlyhave none. Prof. JEAN WALKER MACFARLANE,PH.D.,18 who has studied the value of such tests forpredicting the performance of children who are to be
16. J. exp. Educ. 1948, 17, 309.17. New York Times, Sept. 6, 1953.18. Bull. World Hlth Org. 1953, 9, 409.