Methods of pattern analysis based on statistical signal procedures have been applied to (512-day) records of daily defaecation rate obtained in an ensemble of weanling infants. Careful analysis of the records using several different methods has established the potential significance of the signal. A technique of coherent averaging has produced a stable consistent age-dependent baseline of average behaviour, referred to as an average profile. Extensions have been proposed for the application of statistical methods for the acquisition of standard patterns of diarrhoeal behaviour. Numerical low pass filtering the signal allows a dichotomization of cases, the significance of which is confirmed by differences of class average profiles. Removing the class average profile from the records shows that the majority of cases exhibit consistent individual signal patterns; standardized patterns of behaviour can also be discussed. It is tentatively concluded that objective specification of normal and abnormal defaecation behaviour could be based on spontaneous patterns identified in the records. Several methods have been suggested. Methods similar to those applied here would appear, on the evidence of this study, to be applicable to a variety of other longitudinal epidemiological studies.
The objective specification of the second variable (body weight) measured in an epidemiological field study of weanling diarrhoeal disease of infants has been approached by computer-based pattern analysis, complementing previous studies of the diarrhoeal signal of daily defaecation count (DS). The weight data are available for 64 weeks in a subset of 50 out of 139 infants in the study. A weekly incremental weight signal (IWE) was estimated by successively differencing each new observed weight with a smoothed version of the previous value. Variable latency of the different features of this variable precludes the formation of an average-profile by coherent averaging the ensemble of records; a feature-analysis method based on statistical trend analysis was therefore developed. Features of the resulting IWE average profile can be linked to weanling events, transient diarrhoeal episodes, and typical post-neonatal shifts in level of the diarrhoeal signal. The results are consistent with the view that both nutritional and infectious factors operate in most deviations from typical behaviour seen in individual IWE records. In all the infants having an abnormally low (64 week) weight gain, a sustained abnormal DS elevation can be recognized in the 7-15 week period, with recurrent diarrhoeal episodes (type P2, as previously classified) during the 45-60 week period; both abnormalities were associated with substantial effects on weight gain. But individual P2-diarrhoeal episodes occurring before about 40 weeks of age could be linked only to small, quickly-compensated effects on incremental weight.
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