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disturbed, while a child with a severe ventilatory defect may have minimal emotional disturbance.The design of this study was such that only limited answers could be given to some of the questions asked. The methodology aimed to reduce complex aspects of personality behaviour and family relations to simple reproducible parameters that could be objectively scored on digital coding scales. The advantages and limitations are obvious. When significant differences were found the observations were almost certainly valid but the cut-off points may have been too rigid, so that a complete range of behavioural disturbances and relationships were not revealed. Whether behavioural disturbances were specific to asthma, whether they were consequent on asthma or preceded its development, or whether they were the result of disturbed family relations are important questions which remain unanswered. They will be answered only by specifically designed prospective studies in which asthmatic and control samples of both normal children and children with chronic illness will be randomly selected and the clinical, physiological, and allergic aspects of the asthmatic samples clearly defined.

SummaryThe mean annual prevalence at birth of congenital malformations of the central nervous system for the three years in 48 local authority areas in South Wales was negatively correlated (r = -0X402, P<001) with estimates of the mean total hardness of the related water supplies.The mean annual perinatal mortality rate from anencephalus for the five years 1963-7 in 58 county boroughs in England and Wales was also negatively correlated with estimates of the mean total hardness (r = -0-220, P>00O5) and calcium content (r = -0289, P<005) of the related water supplies.It is concluded that the relationship between these associations may well be secondary. Analytical epidemiological studies of the association are called for.

In a review article on congenital malformations and season of birth, Bailar and Gurian (1965) stated that 'seasonal cycles in births of infants with certain malformations have been demonstrated beyond any reasonable doubt'. Recently, Wehrung and Hay (1970) have referred to the ambiguity of the term 'seasonal ', and Hewitt et al. (1971) (3) secondary-in which the characteristic is associated with season because both characteristic and season are independently related to a certain time of the year (e.g., the end of the tax year; biennial rate demands; school and public holidays). An example of this type of association is the increase in deaths from road traffic accidents at Christmas and other public holidays. It is important to bear these three categories of association in mind since the temporal pattern of variables which are directly or indirectly associated may differ from that of variables which are secondarily associated. While each association could be described as showing 'cyclic' behaviour, the first two (direct and indirect causal) are likely to have a periodic function of one year's duration marked by a varying but smooth pattern which can be fitted to a simple harmonic curve (this we have called harmonic behaviour); while the third (secondary) is likely to have a periodic function of one year's duration marked by a significant change at a particular time of each year for a certain period of time (this we have called periodic non-harmonic behaviour). However, if (on inspection of each year's data) the significant change at a particular time of year (for a certain period of time) is observed for one year only (or appears but irregularly), we would describe the temporal behaviour as episodic.An investigator concerned with the prevalence of congenital malformations who takes 'seasonal' to mean only the direct and indirect categories of association might therefore reasonably consider that fitting an harmonic curve is the appropriate test for a seasonal pattern, but one who includes secondary associations in his definition of seasonal may be justified in using the simple x2 test. If useful hypotheses are to be generated in this field it may be necessary not only to avoid the use of the confusing description 'seasonal' but also to particularize the observed cyclic characteristics of the data studied.

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