PubMed · 1739334
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
M J Healy. 1992. Statistics from the inside. 3. Estimation.. https://doi.org/10.1136/adc.67.1.149
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
In this paper we propose a quasi-exact alternative to the exact unconditional method by Chan and Zhang (1999) estimating confidence intervals for the difference of two independent binomial proportions in small sample cases. The quasi-exact method is an approximation to a modified version of Chan and Zhang's method, where the two-sided p-value of an observation is defined by adding to the one-sided p-value the sum of all probabilities of more "extreme" events in the unobserved tail. We show that distinctively less conservative interval estimates can be derived following the modified definition of the two-sided p-value. The approximations applied in the quasi-exact method help to simplify the computations greatly, while the resulting infringements to the nominal level are low. Compared with other approximate methods, including the mid-p quasi-exact methods and the Miettinen and Nurminen (M&N) asymptotic method, our quasi-exact method demonstrates much better reliability in small sample cases.
Standard deviation and standard error have a clear mutual relationship, but at the same time they differ strongly in the type of information they supply. This can lead to confusion and misunderstandings. Standard deviation describes the variability in a sample of measures of a variable, for instance the variability in ages of the members of a group. It represents the degree to which the values are scattered around their mean: the higher the standard deviation the wider the spread. The value of the standard deviation is not influenced by the number of observations in the sample. The standard error is always used for extrapolation: to estimate the intervals between which the true value of a statistic will occur, based on a sample of observations and with a certain degree of certainty. When interpreting a standard error, it is important to know which statistic (mean, percentage, relative risk, odds ratio) is to be estimated. The value of the standard error is strongly influenced by the number of observations in the sample: the bigger the sample, the smaller the standard error and the more accurate the estimation. To avoid confusion it is recommended to report no longer the standard error of the mean but instead the confidence intervals of the mean to estimate the true value of the mean.
OBJECTIVE: To assess the value of different admission tests in predicting the outcome of small-for-gestational age (SGA) fetuses with normal Doppler waveforms in the umbilical artery. METHODS: Criteria for admission into this retrospective study included: singleton pregnancy with a birth weight < 10th centile; absence of severe maternal complications; no evidence of fetal anomalies on the sonogram; normal umbilical artery Doppler; and availability of complete follow-up. At the first antenatal sonogram classifying the fetus as SGA, Doppler analysis of the uterine and middle cerebral arteries was performed and amniotic fluid volume was assessed. Outcome variables included adverse perinatal outcome (perinatal death, severe morbidity) and emergency Cesarean section for fetal distress. RESULTS: Two hundred and thirty-one pregnancies were included in the study. The mean +/- standard deviation birth weight and gestational age at delivery were 2222 +/- 502 g and 37.3 +/- 2.9 weeks, respectively. In 37 cases (16%), an emergency Cesarean section was performed. There was one intrauterine death and three fetuses delivered by emergency Cesarean section developed severe morbidity. Logistic regression demonstrated that abnormal velocimetry of the uterine arteries and fetal middle cerebral artery were independently correlated with the occurrence of Cesarean section. CONCLUSIONS: SGA fetuses with normal umbilical artery Doppler waveforms and abnormal uterine arteries and fetal middle cerebral artery waveforms have an increased risk of developing distress and being delivered by emergency Cesarean section. Particularly when both uterine and fetal cerebral waveforms are altered at the same time, the risk is exceedingly high (86%) and delivery as soon as fetal maturity is achieved seems advisable. On the other hand, when both vessels have normal waveforms, the chances of fetal distress are small (4%) and expectant management is the most reasonable choice.