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Biomedical subjects

K M Webster

Publications and source records attributed to K M Webster.

4 recordsLinked to original sources
PubMed1997

Nuchal cord evident at birth impacts on fetal size relative to that of the placenta.

We sought to determine whether umbilical cord complications, as evidenced by a nuchal cord at the time of birth, affects birth weight, placental weight and, therefore, the birth to placental weight ratio as a mechanism whereby fetal and placental growth may be differentially affected. The computerized perinatal database of St. Joseph's Health Centre, London, Ontario, was used to obtain the birth weight, placental weight, umbilical cord gases, and nuchal cord status, for all term singleton liveborn infants between January, 1991 and December, 1994. The effect of no nuchal cord versus nuchal cord on birth weight, placental weight, and the birth to placental weight ratio was determined, along with the interactive effects of gestational age and umbilical cord gases, and the 'dose response' effect of the number of cord encirclements. Infants with the cord around the neck were smaller (P < 0.001), their placentas larger (P = 0.001), and their birth to placenta weight ratio also smaller (P < 0.001), with a 'dose response' relationship apparent as these effects were greater in those infants with more than one cord encirclement. Although gestational age and umbilical cord veno-arterial PO2 and PCO2 differences were also found to impact on birth weight, placental weight, and the birth to placental weight ratio, these effects were independent of the effect of nuchal cord complications. Umbilical cord complications is evidenced by a nuchal cord at the time of birth, are associated with a decrease in fetal size relative to that of the placenta, although this is likely to be of little biological significance for most nuchal cord infants.

Analysis of Variance↗
PubMed1993

Age at neonatal death in Ontario, 1979-1987: implications for the interpretation of mortality markers.

Recent evidence concerning time trends in infant mortality rates suggests faster falls in early compared with late deaths. This may be due to rapid advances in neonatal care. This study was undertaken to examine the timing of neonatal death in Ontario between 1979 and 1987. Trends with time, gestational age and type of birth hospital were examined. Evidence suggests that, controlling for level of birth hospital and gestational age, there was a time trend of an increasing proportion of late neonatal deaths. This suggests that early neonatal mortality was decreasing more rapidly than late neonatal mortality. Controlling for year of birth and gestational age, it was observed that the proportion of late neonatal deaths was higher for those born in a tertiary rather than community hospital. In combination, these findings suggest that, due to advances in neonatal care, a disproportionately high number of early neonatal deaths are increasingly being prevented. The findings have implications for the interpretation of routinely available mortality markers. The authors conclude that early neonatal death rate may be becoming a less useful marker and that a measure of perinatal mortality which includes late neonatal deaths would be a useful addition to the currently collected mortality markers.

Data Interpretation, Statistical↗
PubMed1991

Are ordinal models useful for classification?

There is recent interest in classification procedures intended for use only when the response is ordinal. Ordinal response, however, is evident in the parameters estimated by either multinomial logistic or normal discriminant analyses, both of which classify either ordinal or non-ordinal responses. Further, there may be harm in applying ordinal models inappropriately and ample opportunity to assume mistakenly ordinality in real data sets. Therefore, it becomes important to ascertain whether there is benefit obtained in the appropriate application of ordinal models. This paper presents the results of a simulation study designed to compare classification accuracy of various models. We show that ordinal models classify less accurately than the multinomial logistic and normal discriminant procedures under a variety of circumstances. Until further studies become available, we presently conclude that ordinal models confer no advantage when the main purpose of the analysis is classification.

Discriminant Analysis↗