Australian and New Zealand Journal of Psychiatry (1978) 12: 65
BRIEF COMMUNICATIONS
SCHIZOPHRENIA AND SEASON OF BIRTH: FURTHER SOUTHERN HEMISPHERE STUDIES* by GORDON PARKER**
SYNOPSIS Studies in the northern hemisphere and an equatorial region have suggested that schizophrenics have a greater likelihood of being born in the coldest three months of the year. Two further southern hemisphere studies, performed in New Zealand and Tasmania, are reported in this paper. Results from these and other studies suggest that support for a link between schizophrenia and winter birth in the southern hemisphere is slight and inconsistent.
INTRODUCTION A large number of adequately designed studies performed in the northern hemisphere have almost invariably shown a winter excess of births of schizophrenics (Dalen, 1975). One equatorial study has been performed (Parker and Balza, 1977), and a 15% excess above expectation was found in the Philippines for all schizophrenic patients born in the coldest three-month period of the year. In that study, female patients showed a greater seasonal variation than males. Three southern hemisphere studies have been reported so far. In a South African study Dal& (1975) compared month of birth data of 2947 schizophrenic patients born in South Africa with data on birth of South Africans of European descent by month of occurrence since 1921. Dal6n stated that patients were overrepresented in the period May-October (winter-spring) and that that deviation was significant in the sub-group born 194049. Dal6n noted a marked sex difference, with female patients showing the greater seasonal variation. Insufficient data are provided in that study to determine if there was a significant winter excess of female births, but the present author has calculated the 3.8% winter excess for the whole group to be non-significant. In a New South Wales study, Parker and Neilson (1976) compared 2256 schizophrenic patients born in that state with actual dates of birth
* Received 19 September 1977
** Senior Lecturer in Psychiatry, University of New South Wales.
available for each sex of the general population born in New South Wales. No seasonal variation was found for the whole group, nor for male schizophrenics. Female schizophrenics revealed a significant winter excess of 13%, and that winter excess over expectation held true in each decade examined. Krupinski et al. (1976) compared month of birth data of 3919 schizophrenic patients born in Australasia with Victorian data on month of birth for the years 1963-71, and concluded that the notion of a seasonal variation in Australian born schizophrenics was not supported. Comparison by sex was not reported. A methodological weakness of that study was the failure to match geographically the patients and the controls, as Macfarlane (1969) has shown that seasonality of birth varies considerably in Australian states, with conception. curves moving about four months in the year when comparison is made between Tasmania and North Queensland. Krupinski et al. considered that while such studies of schizophrenics often show a statistical seasonal variation, the clinical significance of such results can be questioned. This is at odds with the tenor of comments by researchers such as Hare et al. (1974) who considered that any association between schizophrenia and season of birth would "be the first clear association yet found between a well-defined, objectively measurable environmental factor and the incidence of schizophrenia." Further epidemiological studies of the relationship between schizophrenia in the southern hemisphere would appear warranted and are reported in the present paper.
METHOD Data on schizophrenic patients born in Tasmania and New Zealand were compared with geographically matched control populations. Attempts to perform similar studies in other Australian states not previously studied were unsuccessful, due to difficulties in the extraction of accurate statistical data.
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SCHIZOPHRENIA AND SEASON OF BIRTH
66
TABLE 1 Observed seasonal distributions of schizophrenics’ births compared with expected, by region and by sex. Season Winter
Sep.-Nov. spring
Dec.-Feb. Summer
Mar.-May Autumn
OBS. EXP.
35 28.9
24 29.3
28 28.6
Female
OBS, EXP.
32 30.1
30 30.1
Both
OBS. EXP.
67 59.0
Male
OBS. EXP.
Female Both
J me.-Aug.
Region
Sex
TASMANIA
Male
NEW ZEALAND
*
t
X2*
x2t
29 29.1
2.258
1.701
30 29.8
28 30.0
0.254
0.160
54 59.5
58 58.5
57 59.0
1.665
1.121
232 231.6
245 240.8
212 218.0
223 22 1.6
0.248
0.001
OBS. EXP.
232 227.4
244 238.2
235 214.9
188 218.4
6.345
0.123
OBS. EXP.
464 458.2
489 479.9
447 432.8
41 1 440.1
2.635
0.098
Comparing each season (X2=7.815, df=3,p=O.O5, two-tailed) Comparing winter Season against the remaining nine months (X2=2.706, df=l, p=O.O5, one-tailed)
Information on sex and date of birth was obtained on all
DISCUSSION
236 schizophrenic patients born in Tasmania and who were
Several methodological limitations should be considered first. Seaon of birth data on control populations were less than ideal, as birth registrations rather than birth occurrence dates are most usually collected, and because patient and control groups could not be matched by age. The last point is important as secular changes in seasonality of birth are described in general populations (Cowgill, 1966), and in schizophrenic patients (Shimura et al. 1977).
admitted for the first time to psychiatric institutions in that State from 1970 to 1975. When only the year has been recorded it is the practice for the Australian Bureau of Statistics to classify such patients as having been born on 30th June of that year. To correct a potential anomaly, patients classified as born 30th June were not counted, and an additional 1/29 added to the June figures. Actual dates of birth of the general population are not collected in Tasmania, so that 1969-73 birth registrations by sex in Tasmania by the Australian Bureau of Statistics served as the control. Information on sex and date of birth was obtained on all 1811 schizophrenic patients, born in New Zealand and admitted to psychiatric hospitals in New Zealand for the first time during the years 1972-75, was obtained from the New Zealand Department of Statistics. Birth date by month of occurrence does not exist for New Zealand prior to 1952 and Maori births were not included until 1962. Birth data by month of occurrence and sex for the total population of New Zealand over a ten-year period (196473) were used as the control.
RESULTS Table 1 reveals the seasonal distribution of schizophrenics’ births in the several regions. In Tasmania non-significant winter excesses of 21% for male, and 6% for female, schizophrenics were found. In New Zealand a trend for a winter excess of births of schizophrenics was not suggested. A statistically significant seasonal variation was not found in either region.
A significant winter excess was not found in either of the two regions. This might suggest either that no relationship exists between schizophrenia and winter birth or that statistical significance was not achieved due to small samples. The former possibility is suggested by the New Zealand data, and the latter by the Tasmania data where the winter excess of 13% for the whole group would have achieved significance with a sample in excess of 450. It is difficult to draw conclusions from the Australasian studies when methodological weaknesses make reliable interpretation of data difficult. In particular, inability to match patients and controls by month of birth, due to earlier methods in recording birth data of general populations by the Australian Bureau of Statistics, is seen as presenting a severe limitation. Until studies can be performed which surmount such difficulties, it would appear that support for a link between schizophrenia and winter birth in the southern hemisphere appears slight and inconsistent.
ACKNOWLEDGEMENTS The assistance of Mr A.M. Johnston, of the National Health Statistics Centre, Wellington, and Mr R. Lakin and Mr D.W. Rogers of the Australian Bureau of Statistics, Hobart, in providing data is gratefully acknowledged.
Downloaded from anp.sagepub.com by guest on July 26, 2015
GORDONPARKER
61
tralian and New Zealand Journal of Psychiatry, 1 0
REFERENCES
311.
Cowgill, U. M. (1966). Season of birth in man. Contemporary situation .with special reference to Europe and the southern hemisphere; Ecology, 47: 614. D a l h , P. (1975). Season of Birth. North-Holland Publishing Company. Amsterdam. Hare, E. H., Price, J. S. and Slater, E. (1974). Mental disorder and season of birth: a national sample compared with the general population. British Journal oj Psychiatry, 124: 8 1 . Krupinski, J., Stoller, A. and King, D. (1976). Season of birth in schizophrenia: an Australian study. Aus-
Macfarlane, W. V. (1969). Seasonality of conception in human populations. International Journal of Biometeorology, Supplement 4, 167. Parker, G. and Balza, B. (1977). Season of birth and schizophrenia - an equatorial study. Acta Psychiatrica Scandinavica, 56: 143. Parker, G. and Neilson, M. (1976). Mental disorder and season of birth - a southern hemisphere study. British Journal of Psychiatry; 129: 355. Shimura, M., Nakamura, 1. and Miura, T. (1977). Season of birth of schizophrenics in Tokyo, Japan. Acta Psychiatrica Scandinavica, 55: 225.
Reprint requests to: Dr. Gordon Parker Professorial Unit Rozelle Hospital P.O. Box 1 Rozelle, NSW 2039 Downloaded from anp.sagepub.com by guest on July 26, 2015
BRIEF COMMUNICATIONS
SCHIZOPHRENIA AND SEASON OF BIRTH: FURTHER SOUTHERN HEMISPHERE STUDIES* by GORDON PARKER**
SYNOPSIS Studies in the northern hemisphere and an equatorial region have suggested that schizophrenics have a greater likelihood of being born in the coldest three months of the year. Two further southern hemisphere studies, performed in New Zealand and Tasmania, are reported in this paper. Results from these and other studies suggest that support for a link between schizophrenia and winter birth in the southern hemisphere is slight and inconsistent.
INTRODUCTION A large number of adequately designed studies performed in the northern hemisphere have almost invariably shown a winter excess of births of schizophrenics (Dalen, 1975). One equatorial study has been performed (Parker and Balza, 1977), and a 15% excess above expectation was found in the Philippines for all schizophrenic patients born in the coldest three-month period of the year. In that study, female patients showed a greater seasonal variation than males. Three southern hemisphere studies have been reported so far. In a South African study Dal& (1975) compared month of birth data of 2947 schizophrenic patients born in South Africa with data on birth of South Africans of European descent by month of occurrence since 1921. Dal6n stated that patients were overrepresented in the period May-October (winter-spring) and that that deviation was significant in the sub-group born 194049. Dal6n noted a marked sex difference, with female patients showing the greater seasonal variation. Insufficient data are provided in that study to determine if there was a significant winter excess of female births, but the present author has calculated the 3.8% winter excess for the whole group to be non-significant. In a New South Wales study, Parker and Neilson (1976) compared 2256 schizophrenic patients born in that state with actual dates of birth
* Received 19 September 1977
** Senior Lecturer in Psychiatry, University of New South Wales.
available for each sex of the general population born in New South Wales. No seasonal variation was found for the whole group, nor for male schizophrenics. Female schizophrenics revealed a significant winter excess of 13%, and that winter excess over expectation held true in each decade examined. Krupinski et al. (1976) compared month of birth data of 3919 schizophrenic patients born in Australasia with Victorian data on month of birth for the years 1963-71, and concluded that the notion of a seasonal variation in Australian born schizophrenics was not supported. Comparison by sex was not reported. A methodological weakness of that study was the failure to match geographically the patients and the controls, as Macfarlane (1969) has shown that seasonality of birth varies considerably in Australian states, with conception. curves moving about four months in the year when comparison is made between Tasmania and North Queensland. Krupinski et al. considered that while such studies of schizophrenics often show a statistical seasonal variation, the clinical significance of such results can be questioned. This is at odds with the tenor of comments by researchers such as Hare et al. (1974) who considered that any association between schizophrenia and season of birth would "be the first clear association yet found between a well-defined, objectively measurable environmental factor and the incidence of schizophrenia." Further epidemiological studies of the relationship between schizophrenia in the southern hemisphere would appear warranted and are reported in the present paper.
METHOD Data on schizophrenic patients born in Tasmania and New Zealand were compared with geographically matched control populations. Attempts to perform similar studies in other Australian states not previously studied were unsuccessful, due to difficulties in the extraction of accurate statistical data.
Downloaded from anp.sagepub.com by guest on July 26, 2015
SCHIZOPHRENIA AND SEASON OF BIRTH
66
TABLE 1 Observed seasonal distributions of schizophrenics’ births compared with expected, by region and by sex. Season Winter
Sep.-Nov. spring
Dec.-Feb. Summer
Mar.-May Autumn
OBS. EXP.
35 28.9
24 29.3
28 28.6
Female
OBS, EXP.
32 30.1
30 30.1
Both
OBS. EXP.
67 59.0
Male
OBS. EXP.
Female Both
J me.-Aug.
Region
Sex
TASMANIA
Male
NEW ZEALAND
*
t
X2*
x2t
29 29.1
2.258
1.701
30 29.8
28 30.0
0.254
0.160
54 59.5
58 58.5
57 59.0
1.665
1.121
232 231.6
245 240.8
212 218.0
223 22 1.6
0.248
0.001
OBS. EXP.
232 227.4
244 238.2
235 214.9
188 218.4
6.345
0.123
OBS. EXP.
464 458.2
489 479.9
447 432.8
41 1 440.1
2.635
0.098
Comparing each season (X2=7.815, df=3,p=O.O5, two-tailed) Comparing winter Season against the remaining nine months (X2=2.706, df=l, p=O.O5, one-tailed)
Information on sex and date of birth was obtained on all
DISCUSSION
236 schizophrenic patients born in Tasmania and who were
Several methodological limitations should be considered first. Seaon of birth data on control populations were less than ideal, as birth registrations rather than birth occurrence dates are most usually collected, and because patient and control groups could not be matched by age. The last point is important as secular changes in seasonality of birth are described in general populations (Cowgill, 1966), and in schizophrenic patients (Shimura et al. 1977).
admitted for the first time to psychiatric institutions in that State from 1970 to 1975. When only the year has been recorded it is the practice for the Australian Bureau of Statistics to classify such patients as having been born on 30th June of that year. To correct a potential anomaly, patients classified as born 30th June were not counted, and an additional 1/29 added to the June figures. Actual dates of birth of the general population are not collected in Tasmania, so that 1969-73 birth registrations by sex in Tasmania by the Australian Bureau of Statistics served as the control. Information on sex and date of birth was obtained on all 1811 schizophrenic patients, born in New Zealand and admitted to psychiatric hospitals in New Zealand for the first time during the years 1972-75, was obtained from the New Zealand Department of Statistics. Birth date by month of occurrence does not exist for New Zealand prior to 1952 and Maori births were not included until 1962. Birth data by month of occurrence and sex for the total population of New Zealand over a ten-year period (196473) were used as the control.
RESULTS Table 1 reveals the seasonal distribution of schizophrenics’ births in the several regions. In Tasmania non-significant winter excesses of 21% for male, and 6% for female, schizophrenics were found. In New Zealand a trend for a winter excess of births of schizophrenics was not suggested. A statistically significant seasonal variation was not found in either region.
A significant winter excess was not found in either of the two regions. This might suggest either that no relationship exists between schizophrenia and winter birth or that statistical significance was not achieved due to small samples. The former possibility is suggested by the New Zealand data, and the latter by the Tasmania data where the winter excess of 13% for the whole group would have achieved significance with a sample in excess of 450. It is difficult to draw conclusions from the Australasian studies when methodological weaknesses make reliable interpretation of data difficult. In particular, inability to match patients and controls by month of birth, due to earlier methods in recording birth data of general populations by the Australian Bureau of Statistics, is seen as presenting a severe limitation. Until studies can be performed which surmount such difficulties, it would appear that support for a link between schizophrenia and winter birth in the southern hemisphere appears slight and inconsistent.
ACKNOWLEDGEMENTS The assistance of Mr A.M. Johnston, of the National Health Statistics Centre, Wellington, and Mr R. Lakin and Mr D.W. Rogers of the Australian Bureau of Statistics, Hobart, in providing data is gratefully acknowledged.
Downloaded from anp.sagepub.com by guest on July 26, 2015
GORDONPARKER
61
tralian and New Zealand Journal of Psychiatry, 1 0
REFERENCES
311.
Cowgill, U. M. (1966). Season of birth in man. Contemporary situation .with special reference to Europe and the southern hemisphere; Ecology, 47: 614. D a l h , P. (1975). Season of Birth. North-Holland Publishing Company. Amsterdam. Hare, E. H., Price, J. S. and Slater, E. (1974). Mental disorder and season of birth: a national sample compared with the general population. British Journal oj Psychiatry, 124: 8 1 . Krupinski, J., Stoller, A. and King, D. (1976). Season of birth in schizophrenia: an Australian study. Aus-
Macfarlane, W. V. (1969). Seasonality of conception in human populations. International Journal of Biometeorology, Supplement 4, 167. Parker, G. and Balza, B. (1977). Season of birth and schizophrenia - an equatorial study. Acta Psychiatrica Scandinavica, 56: 143. Parker, G. and Neilson, M. (1976). Mental disorder and season of birth - a southern hemisphere study. British Journal of Psychiatry; 129: 355. Shimura, M., Nakamura, 1. and Miura, T. (1977). Season of birth of schizophrenics in Tokyo, Japan. Acta Psychiatrica Scandinavica, 55: 225.
Reprint requests to: Dr. Gordon Parker Professorial Unit Rozelle Hospital P.O. Box 1 Rozelle, NSW 2039 Downloaded from anp.sagepub.com by guest on July 26, 2015
