Brit. J. prev. soc. Med. (1960), 14, 139-147 MORTALITY FROM CEREBROVASCULAR ACCIDENTS AND HYPERTENSION IN THE REPUBLIC OF IRELAND BY ROY M. ACHESON* From the Department of Social Medicine, Trinity College, Dublin It is well known that hypertension may be associated with certain cerebrovascular accidents on the one hand, and with coronary heart disease on the other. The fact that two diseases tend to occur together in one patient, however, does not necessarily mean that they are similar in their epidemiology or mortality. A study of the mortality from coronary artery disease in the Republic of Ireland over the past 30 years has recently been published from this department (Acheson and Thornton, 1958), and it was felt that it might be instructive to undertake similar analyses of the vital statistics of the Republic for hypertension and cerebrovascular accidents and to compare them with those already published for coronary artery disease. Although it is recognized that mortality figures are a poor index of the prevalence of hypertension (W.H.O., 1959), they are probably a fair index of the incidence of cerebro- vascular accidents taken as a group. DATA The Irish data are again drawn from the annual reports of the registration of births, marriages, and deaths in the Republic of Ireland from 1926 to 1957, prepared on behalf of the Registrar General. The classification of cause of death is made in accor- dance with the International Statistical Classifica- tion, which has been changed three times since 1926. It proved impossible to obtain any continuity over the entire period in respect of hypertension, but some continuity has been obtainable for cerebro- vascular accidents. The exact details of the list numbers adopted for the present study are presented in Table 1. TABLE I DESCRIPTION OF DISEASES CLASSIFIED AS HYPERTENSION AND CEREBROVASCULAR ACCIDENTS Inter- national Cerebrovascular Classifi- Hypertension Accidents cation 1926-1930 74a Cerebral Haemor- (Third rhage, Apoplexy Revision) 74b Cerebral Thrombosis and Embolism 75a Hemiplegia 1931-1939 102 Idiopathic Abnor- 82a Cerebral Haemor- (Fourth malities of Blood rhage Revision) Pressure b Cerebral Thrombosis, Embolism c Cerebral Softening d Hemiplegia 1940-1949 83 Intracranial Lesions (Fifth of Vascular Origin Revision) 1950-1956 440 EssentialBenign Hy- 331 Cerebral Haemor- (Sixth pertension with rhage Revision) Heart Disease 332 Cerebral Embolus and 441 Essential Malignant Thrombosis Hypertension with Heart Disease 442 Hypertensive Heart Disease with Arteri- olar Nephrosclerosis 443 Other and Unspeci- fied Hypertensive Heart Disease 444 Essential Benign Hy- pertension without mentions of Heart 445 Essential Malignant Hypertension with- out mention of Heart 446 Hypertension with Arteriolar Nephro- sclerosis without mention of I leart 447 Other Hypertensive Disease without mention of Heart 139 * Present address London School of Hygiene and Tropical Medi- cine, Keppel Street, London, W.C.I.
Transcript
Brit. J. prev. soc. Med. (1960), 14, 139-147
MORTALITY FROM CEREBROVASCULAR ACCIDENTS
AND HYPERTENSION IN THE REPUBLIC OF IRELAND
BY
ROY M. ACHESON*
From the Department ofSocial Medicine, Trinity College, Dublin
It is well known that hypertension may beassociated with certain cerebrovascular accidents onthe one hand, and with coronary heart disease on theother. The fact that two diseases tend to occurtogether in one patient, however, does not necessarilymean that they are similar in their epidemiology ormortality. A study of the mortality from coronaryartery disease in the Republic of Ireland over thepast 30 years has recently been published from thisdepartment (Acheson and Thornton, 1958), and itwas felt that it might be instructive to undertakesimilar analyses of the vital statistics of the Republicfor hypertension and cerebrovascular accidents andto compare them with those already published forcoronary artery disease. Although it is recognizedthat mortality figures are a poor index of theprevalence of hypertension (W.H.O., 1959), they areprobably a fair index of the incidence of cerebro-vascular accidents taken as a group.
DATA
The Irish data are again drawn from the annualreports of the registration of births, marriages, anddeaths in the Republic of Ireland from 1926 to 1957,prepared on behalf of the Registrar General. Theclassification of cause of death is made in accor-dance with the International Statistical Classifica-tion, which has been changed three times since 1926.It proved impossible to obtain any continuity overthe entire period in respect of hypertension, butsome continuity has been obtainable for cerebro-vascular accidents. The exact details of the list
numbers adopted for the present study are presentedin Table 1.
442 Hypertensive HeartDisease with Arteri-olar Nephrosclerosis
443 Other and Unspeci-fied HypertensiveHeart Disease
444 Essential Benign Hy-pertension withoutmentions of Heart
445 Essential MalignantHypertension with-out mention of Heart
446 Hypertension withArteriolar Nephro-sclerosis withoutmention of I leart
447 Other HypertensiveDisease withoutmention of Heart
139
* Present address London School of Hygiene and Tropical Medi-cine, Keppel Street, London, W.C.I.
ROY M. ACHESON
x
0z
1. 5
-i4
I.-
cc0 1. 0-
I>
40.50
o.
MALES
4 tO. o l 1 1
1926 1930 1935 1940 1945
YEAR
FEMALES
t11950 1955 1926 1930 1935
I I
1940 1945 1950 1955
Y E A R
FIG. 1.-Comparative mortality indices for both sexes for cerebro-vascular accidents in the Republic of Ireland, 1926 to 1956.
It will be noted that the International List hasnever distinguished cerebral embolus and cerebralthrombosis, and that for the present purpose thesetwo diagnoses have been grouped with cerebralhaemorrhage.
SECULAR TREND
Comparative mortality indices (C.M.Is.) taking1938 as unity, are shown for both sexes for cerebro-vascular accidents in Fig. 1. There is a slight secularincrease between 1926 and 1949, the index risingfrom 0 9 to 1 -3 in both sexes. Between 1950 and1956, however, the increase is much more rapid,rising from 1 - 3 to 1 * 8 in both sexes.
Changes in the International List have made itimpossible to calculate the comparative mortalityindices for hypertension. The age-specific deathrates for each of the years from 1950 to 1956, how-ever, suggest that during this time, at least, there hasbeen little change in any but the oldest age groupswhere there has been more than a three-fold increasein both sexes (see Table II).
AGE INCIDENCE
Age-specific death rates for cerebrovascular acci-dents in each of the three decades between 1926 and1956 are shown in Table III (opposite). When thedecades are compared, there has been a tendency, par-ticularly in the post war period, for the death rates tofall in females aged under 54 and to rise in both sexesin the oldest age groups. With the exception of those
aged 75 and over in the first decade, and in those aged85 and over in the other two decades, there is in bothsexes a steady upward gradient in death rates foreach of the quinquennial age groups in each decade.Table II shows that there is also a steady upwardgradient with age for mortality from hypertension.
SEX DIFFERENCESThe sex ratios for each of the three decades are
i -+ I . l
140
~ I
MORTALITY FROM CEREBROVASCULAR ACCIDENTS
TABLE III
AVERAGE ANNUAL DEATHS PER 100,000 FROM CEREBROVASCULAR ACCIDENTS
141
Index takingSex Age Group (yrs) Average Annual Death Rate Indices taking 1926-35 as Unity 1935-45 as
Unity
Year ...1926-35 1936-45 1946-55 1936-45 1946-55 1946-55
shown by quinquennial age groups for cerebrovascu-lar accidents in Table IV. At all ages and at all timesthis has been a commoner certified cause of deathin females than in males. The sex difference ismost marked in the youngest groups and becomessteadily less until the ratio approaches unity in theoldest groups. There is remarkably little seculartrend in the sex ratio at any age group.
Table V shows the sex ratios for hypertension forthe period during which comparable statistics areavailable; with the exception of the youngest groups,where the death rates are very low, and the groupsaged 55-64, hypertension also seems to be a common-er certified cause of death in females than in males,but there is no comparable tendency for the ratio toincrease with age.
GEOGRAPHICAL DIFFERENCES WITHIN THE REPUBLICOF IRELAND
Death rates for the period 1951 to 1955 stan-dardized to the population in 1951 for the countiesand county boroughs in the Republic are shown inTable VI and Fig. 2, and in Figs 3 and 4 (opposite).
TABLE VIAVERAGE ANNUAL DEATH RATES PER 100,000 (AT AGE
35+) FOR COUNTIES AND BOROUGHS, 1951-1955STANDARDIZED TO THE POPULATION IN 1951, BY SEX
Although it might be maintained that the urbandeath rate from cerebrovascular accidents is on theaverage a little higher than the rural death rate fromthis cause, and that death rates in the south-east arehigher than those in the north-west, there is no verystrongly defined geographical pattern, nor is there avery wide range of variation. The highest death rate(369 for women in County Wicklow) is only threeand a half times higher than the lowest (107 forwomen in County Longford). In the case of hyper-tension, although the rates are on the whole muchlower, the range of variation is much the same, therate of 140 for males in Dun Laoghaire being 3-7times higher than the rate of 38 for males in Water-ford County Borough; but the overall pattern seemsto be even less clearly defined.
FIG. 2.-Key to counties and boroughs in Figs 3 and 4.
OCCUPATION AND INCOMECauses of death are not published by trade and
occupation in the Republic because the necessarysocial classification offers considerable technicaldifficulties. It has not therefore been possible toanalyse the present data in terms of social status oroccupational hazard.
COMPARISON OF MORTALITY FROM CEREBROVASCULARACCIDENTS AND HYPERTENSION IN THE REPUBLIC OF
IRELAND WITH THAT IN OTHER COUNTRIESTables VII and VIII (overleaf) show death rates
for the two groups for various countries in 1955,standardized against the Irish population in 1951,the countries being ranked in order of the maledeath rates. Three aspects of these Tables are worthyof comment; first, the lowest death rate fromcerebrovascular accidents is considerably higherthan the highest death rate ascribed to hypertension;secondly, although the sex ratio for cerebrovascularaccidents does not range appreciably from unity forany of the countries, if the countries had beenranked according to female death rates the orderwould change a great deal-for example, Swedenwould rise from eleventh to fourth position, andFrance would fall from eighth to fifteenth. In thecase of hypertension it is also true that the order ofranking by female death rates would be quitedifferent from that by male death rates, but this is
142
FIG. 3.-As
MORTALITY FROM CEREBROVASCULAR ACCIDENTS 143
CEREBROVASCULAR DISEASE
El3 upder 140
0E 140 179 FEMALES180-219
220-259
260-299
*300-339
U340 L over
average annual death rates, 1951-1955, from cerebrovascular disease, by counties and boroughs (see alsoTable VI). The scheme used for shading is the same for both sexes.
HYPERTENSIONso4 ?> Elunder 60
(D60-79 FEMALES
= 80-99
E 100-119
FIG. 4.-Average annual death rates, 1951-1955, from hypertension by counties and boroughs (see alsoTable VI). The scheme used for shading is the same for both sexes.
ROY M. ACHESON
less surprising because the sex ratio varies rathermore widely than in Table VII and there is very littledifference between the male rates for the first ninecountries.
TABLE VIIDEATH RATES PER 100,000 FROM CEREBROVASCULARDISEASE (AT AGE 40+) FOR VARIOUS COUNTRIES IN 1955
(STANDARDIZED TO IRISH POPULATION, 1951)
SexCountry Ratio M/F
Male Female
1. Japan2. Finland3. Italy4. Scotland5. England and Wales6. Switzerland7. Australia8. France9. U.S.A.10. Denmark11. Sweden12. Norway13. Netherlands14. Canada15. New Zealand16. Ireland
774476465440421393378378342338331324319318294250
611511413538412402428307336386478371380343395301
1 *30 91-10-81.01.00 9
_____________ 1
TABLE VIIIDEATH RATES PER 100,000 FROM HYPERTENSION (AT AGE40+) FOR VARIOUS COUNTRIES IN 1955 (STANDARDIZED
TO IRISH POPULATION, 1951)
SexCountry Ratio M/F
Male Female
1. England and Wales 128 109 1-22. U.S.A. .120 172 0 73. Australia 118 125 0 94. Ireland 112 120 0 95. -Scotland 112 107 1*06. Finland 104 196 0* 57. Canada 104 136 0- 88. New Zealand 101 129 0-89. Italy 93 109 0-8
CORRELATION BETWEEN DEATHS FOR CEREBRO-VASCULAR ACCIDENTS, HYPERTENSION, AND
CORONARY ARTERY DISEASEIn order to investigate further the interrelation-
ships between the mortality patterns of the twodiseases being studied here and that of coronaryartery disease, a correlation analysis was carried outbetween the standardized death rates shown inTables VI, VII and VIII above and those in TablesIV and VI in the earlier publication (Acheson andThornton, 1958). The results are given in TablesIX, X, and XI.
Table IX shows that, despite the variations in sexratio referred to above, the mortality in the twosexes for each of the three diseases is highly corre-lated both inside Ireland and in the comparison
between Ireland and other countries. The correla-tions tend to be higher in the international com-parison than inside Ireland, but in each case th'ey arehighest for coronary artery disease. The cross-correlations between the three diseases insideIreland are given in Table X which shows that allthe correlations for males are higher than those forfemales; in females the highest correlation is thatbetween coronary artery disease and hypertension,and the male correlation between these two diseasesis also high. However, the correlations between theother diseases for both sexes are positive, and (withthe exception of those shown between cerebro-vascular accidents and hypertension for females) theyare significant at the 5 per cent. level at the least.
1-21.0
0 9 TABLE IX0 7 CORRELATION BETWEEN MALE AND FEMALE STAN-0 9 DARDIZED DEATH RATES FOR THE 32 IRISH COUNTIES0 8 AND FOR THE 16 COUNTRIES SHOWN IN TABLES VII AND
0-832 Irish Counties 16 Countries
Cause of Death and Boroughs, shown in Tables1951-1955 VII and VIII
The international analyses (see Table XI) alsoshow that the highest correlation in both sexes isthat between coronary artery disease and hyper-tension. Beyond this, however, there is little further
144
MORTALITY FROM CEREBROVASCULAR ACCIDENTS
similarity between Tables X and XI, for the inter-national analysis fails to demonstrate any correla-tion between cerebrovascular accidents and hyper-tension for either sex, and such correlation asexists between cerebrovascular disease and coronaryartery disease is negative, whereas in Ireland it ispositive.
DISCUSSIONBefore attempting to evaluate the positive findings
made in this study, the shortcomings of the datashould be stressed. Cerebrovascular accidents mostcommonly involve the middle cerebral artery, andresult in hemiparesis or hemiplegia. Of all causes ofdeath, apoplexy with hemiplegia is probably theeasiest to distinguish. and therefore carries the leastobserver error in certification. Yet this apparentsimplicity in diagnosis is most deceptive because,while the classical apoplexy is usually caused byhaemorrhage, the haemorrhage may be into thebrain stem, or the lesion may be due to a thrombusof any of a number of arteries. Furthermore, analmost identical clinical picture may develop as aconsequence of embolism, a lesion of quite distinctaetiology from haemorrhage or thrombosis. Thearrangement of the International List has made itimpossible to distinguish between the three, partlybecause, throughout the period studied, cerebralthrombosis and cerebral embolism have always beengrouped together, and partly because between 1926and 1939 the supplementary heading of hemiplegiawas offered. Thus, under the heading of cerebro-vascular accidents, we are really considering threedistinct diseases which may produce a single clinicalpattern; the latter misleadingly obvious to doctorand layman alike.
Hypertension, on the other hand, can be diagnosedwith certainty in the home (where most deaths occur)only by the use of a sphygmomanometer while thepatient is alive. Very often, moreover, there is a fallin blood pressure in agonal heart failure, so that adoctor attending the last illness may not realize thatthe blood pressure was previously raised, with theresult that death is ascribed to "cardiac failure" or"myocardial degeneration" without any mention ofhypertension. Thus, many hundreds of deaths whichwere in fact due to hypertension must appear amongthe 4,965 classified as caused by "other myocardialdegeneration" (Int. List No. 422) out of a total of10,902 cardiac deaths in the Republic of Ireland in1956.A further difficulty stems from the fact that, even
in cases in which the hypertension has been recog-nized, it may be listed on the death certificate as acontributary cause of death, or as a complication,
rather than as the disease which is really respon-sible for death. In many countries, therefore, it willnot appear in the national vital statistics. Broderick(1955), in a detailed analysis of death certificates inthe county borough of Dublin, has shown that this isindeed the case. During the year 1952 a total of 310deaths was certified as due to hypertension (Int. ListNos. 440 447). In a further 386 certificates, however,hypertension appeared as a complication or as acontributory cause of death. In 134 of these casescerebral haemorrhage (Int. List No. 331) was certifiedas being the underlying disease directly responsiblefor death and in 102 cases coronary artery disease(Int. List No. 420). On the one hand, this evidenceindicates that the published mortality from hyper-tension underestimates the prevalence of the diseaseby a factor of two at least; on the other hand, itamply supports the statement made at the beginningof this paper that cerebral vascular disease andcoronary artery disease are commonly complicatedby hypertension. Thus, statistics compiled fromdeath certificates will tend to underestimate theprevalence of hypertension.A further complication is that the degree of
underestimation of the prevalence of hypertensionwill vary from place to place depending, among otherthings, on the national laws and practices concerningthe completion of the death certificate and the codingof the cause of death. These in turn will depend onthe medical tradition in the schools where thedoctors were trained, on their knowledge of themethods of their national departments of vitalstatistics, and on their understanding of the im-portance of imparting accurate standardized in-formation. National differences will depend too uponthe extent to which the authorities confine theirinterest in the death certificate solely to the rulingout of foul play and how much to the compilation ofaccurate mortality statistics. W.H.O. has attemptedto do away with such idiosyncrasies by drawing up astandard form of death certificate and by publishinga manual of rules for abstracting information fromcertificates on which several causes of death appear(W.H.O., 1948). Both of these are used by manymember countries, including Ireland. Other mattersof importance are the proportion of the populationwhich dies in hospital, and the amount the doctorcertifying the death knows about his patient. It is,therefore, perhaps a little incongruous that theInternational List should offer six sub-groups for theclassification of hypertension which may require thediagnostic facilities of a hospital for their identifica-tion, and yet should fail to separate cerebralembolism and thrombosis which can often bedistinguished by careful history-taking.
145
ROY M. ACHESON
The findings in the present analysis will have to beconsidered, these shortcomings being borne in mind.If it is accepted that the rise in comparative mortalityindices for cerebrovascular disease in the Republicof Ireland in both sexes in 1931, 1940, and 1950 aredue to changes in the International List, the moststriking characteristic of Figs 1 and 2 is the extra-ordipary steadiness of these indices between 1926 and1950. During the final 6 years, however, there can belittle doubt that a genuine rise has taken place. Muchif not all of this rise is probably due to improvementin the collection of statistics. During this time therehas been a drive in the more rural and isolated partsof the Republic to ensure that all deaths are properlycertified, with the result that there has been a verysharp fall in the numbers of deaths ascribed tosenility or remaining uncertified (for further detailssee Acheson and Thornton, 1958). This trend is alsoreflected in Tables II and III, where the apparent risein death rates from hypertension as well as fromcerebrovascular disease among the older age groupsmust also be largely, if not entirely, due to moreaccurate certification.The secular fall in the death rate from cerebro-
vascular accidents in women aged 35-54 is morelikely to be real. One possible cause of this is thedecrease in the number of cases of rheumatic heartdisease, a decrease which is reflected in the fact thatthe death rates from this cause in Ireland have beenalmost halved during the 30 years under considera-tion. Therefore, deaths from cerebral embolism havepresumably fallen too, because cerebral embolism isvery often associated with rheumatic carditis, and ismore likely to develop in young women than in oldpeople of either sex. The available statistics are not,however, suitable for examining this hypothesis inany detail.The most interesting aspect of the geographical
data is the correlation analysis shown in Tables IXto XI. Evidently there is no great discrepancy inIreland, or in the other countries studied, betweendeath rates in the two sexes, for the between sexcorrelations vary from 0 75 to 0 94. The value of0 94 for coronary artery disease can be interpretedas giving indirect supportive evidence for theconclusion, drawn from the Irish comparativemortality indices (Acheson and Thornton, 1958),that the rate of increase in female death rates fromthis disease has been as rapid as that in male deathrates. It can also be looked upon as a reflection ofthe accuracy of diagnosis, however, for Tables X andXI show that the only consistently high correlationsare those between coronary artery disease and hyper-tension. It could well be argued that a similar type ofmodus vivendi or environment is a contributory
factor to causing death from the two diseases. Onthe other hand, these diseases require refinedmedical techniques for their diagnosis, and theobserved correlation may really reflect the standardof medical care. In the previous paper (Acheson andThornton, 1958), it was concluded that the increasein mortality from coronary artery disease was notentirely attributable to improved diagnostic methods.This is not to say, however, that the level of medicalskill in a community has no bearing on the certifieddeath rate from coronary artery disease; it certainlymust have some bearing, as indeed it must on thecertified death rate from hypertension. Furthermore,as Tables VI, VII, and VIII show, the geographicalareas both inside and outside Ireland with thehighest mortality from these causes tend to be thosewith the most highly developed medical services;thus, although the social culture which Morris (1955)has dubbed the "Western" way of life may causepeople to die from hypertension, as it is known tocause them to die from coronary artery disease, thestatistical relationship found between the death ratesfrom the two causes in the present study is more thanlikely to be also a reflection of diagnosis andcertification.There is a wide difference in the correlation be-
tween cerebrovascular disease and hypertension orcoronary disease shown in Table X as comparedwith that shown in Table XI. In Ireland the areaswith high death rates for one of the three certifiedcauses of death tend to have high death rates for theother two, particularly in males. In the internationalcomparison this is clearly not the case, the moststriking difference being that Japanese males showthe highest standardized death rate for cerebro-vascular disease and the lowest for coronary arterydisease (see Acheson and Thornton, 1958). Whilesuch discrepancies between one country and anothermay to some extent be due to true differences in theepidemiology of disease, variations in diagnostic andstatistical technique cannot be ruled out as animportant contributary factor.Few facts of epidemiological value have resulted
from this analysis. It does, however, illustrateadmirably the pressing need (stated by W.H.O.,1959) for a thorough scientific study of the methodswhereby vital statistics are collected all over theworld.
SUMMARY(1) Between 1926 and 1956 comparative mortality
indices for both sexes in the Republic of Irelandshow a rise for cerebrovascular accidents. This isprobably entirely due to changes in the InternationalClassification of Causes of Death and to more
146
MORTALITY FROM CEREBROVASCULAR ACCIDENTS
accurate certification of death. A similar study of thesecular trend in mortality from hypertension wasimpossible because of alterations in the InternationalList; between 1950 and 1956 however, there was nosuggestion of consistent change, except in the oldestgroups where death rates rose but certification hasimproved.
(2) Both cerebrovascular accidents and hyperten-tion were more commonly certified as causing deathin women than in men.
(3) In respect of cerebrovascular disease, theaverage standardized death rates for the period1950-1955 tended to be higher in urban than in ruraldistricts; they also tended to be higher in the countiesof the eastern seaboard than elsewhere in the ruralparts of the Republic. For hypertension the averagestandardized death rates for the conurbation ofDublin were higher than those elsewhere in theRepublic; otherwise there was little consistentgeographical pattern.
(4) Of sixteen countries whose vital statistics areregularly published by W.H.O., Ireland in 1955 hadthe fourth highest male death rate from hypertensionbut the lowest from cerebrovascular accidents-alldeath rates being standardized to the Irish popula-tion in 1951.
(5) A correlation analysis was carried out betweendeath rates for hypertension, cerebrovascular acci-dents, and coronary artery disease for the 32 ad-ministrative areas inside Ireland and for Ireland andthe other fifteen countries, with the following results:
(a) There were high positive correlations betweenthe sexes for all three diseases, the highest cor-relation in each analysis being that for coro-nary heart disease (-083 in Ireland and+0 94 in the International comparison).
(b) There was a highly significant correlation be-tween hypertension and coronary artery diseaseboth inside Ireland and internationally.
(c) Inside Ireland the other correlations were posi-tive, and the only one which was not significantwas that between cerebrovascular accidentsand hypertension for females.
(d) In the international comparison, correlationsbetween cerebrovascular accidents and hyper-tension differed little from zero, and thosebetween coronary artery disease and cerebro-vascular disease were negative.
(6) In considering the possible significance of thesefindings, the grave shortcomings of mortality figuresfor cerebrovascular accidents and hypertension as abasis for epidemiological studies are stressed.
I am most grateful to Miss Marie Geoghegan who borethe brunt of the computing; to Dr. Donal MacCarthyand Mr. J. F. Knaggs of the Central Statistics Office,Dublin for making available unpublished data; and toProf. W. J. E. Jessop for encouragement. Prof. W. S.Walton kindly read the text. The research was support-ed by a grant from the Medical Research Council ofIreland.
REFERENCESAcheson, R. M., and Thornton, E. H. (1958). Brit. J. prey. soc. med.,
12, 82.Broderick, J. B. (1955). 'Classification of Multiple Causes of Death".
Unpublished report to W.H.O. National Committees on Vital andHealth Statistics.
Department of Health, Ireland (1955, 1957). "Reports on VitalStatistics for 1953 and 1954". Central Statistics Office, Dublin.- (1946-1954). "Annual Reports of the Registrar-General for the
Years, 1945-1952". Central Statistics Office, Dublin.Department of Local Government and Public Health, Ireland (1927-
1945). "Annual Reports of the Registrar-General for the Years1926-1944". Central Statistics Office, Dublin.
Morris, J. N. (1955). Med. Offr., 94, 251.World Health Organization (1948). "Manual of the International
Statistical Classification of Diseases, Injuries, and Causes of Death",vol. 1, p. 368. W.H.O., Geneva.
