Confidence of compliance: a Bayesian approach for percentile standards.

Rules for assessing compliance with percentile standards commonly limit the number of exceedances permitted in a batch of samples taken over a defined assessment period. Such rules are commonly developed using classical statistical methods. Results from alternative Bayesian methods are presented (using beta-distributed prior information and a binomial likelihood), resulting in "confidence of compliance" graphs. These allow simple reading of the consumer's risk and the supplier's risks for any proposed rule. The influence of the prior assumptions required by the Bayesian technique on the confidence results is demonstrated, using two reference priors (uniform and Jeffreys') and also using optimistic and pessimistic user-defined priors. All four give less pessimistic results than does the classical technique, because interpreting classical results as "confidence of compliance" actually invokes a Bayesian approach with an extreme prior distribution. Jeffreys' prior is shown to be the most generally appropriate choice of prior distribution. Cost savings can be expected using rules based on this approach.

Does age or sex affect pharyngeal swallowing?

The influence of age and gender on the pharyngeal pressure wave during swallowing was investigated in 73 healthy volunteers using a four-sensor manometry probe. The distal sensor was placed within the upper oesophageal sphincter (UOS) and three proximal sensors were located in the pharynx 2, 4 and 6 cm above the UOS. Twenty-nine variables describing the amplitude and timing of the swallow waveforms for a 5 ml water bolus were recorded from the pharynx and the UOS. Analysis of the results indicated that aging was associated with slowing of the swallow response in the pharynx, impaired opening of the UOS and a marked reduction in resting UOS tone.

Giant cell tumour of the temporal bone presenting as vertigo.

We report a case of giant cell tumour of the temporal bone arising in a 31-year-old man. The presenting symptoms were unusual, being rotational vertigo, unilateral tinnitus, and hearing loss. A computed tomography (CT) scan showed a large mass within the right temporal bone and the infratemporal fossa. The radiological appearance was suggestive of an aggressive primary neoplasm arising within bone. Biopsy and subsequent resection showed a giant cell tumour of bone. The tumour was histological grade 1. At two-year follow-up, there was no evidence of tumour recurrence or metastasis.

Patchy distributions: Optimising sample size.

A method for estimating sample size which does not require an a priori definition of desired precision, or the assumption that the population is normally distributed with constant variance, has recently been proposed. This paper discusses this method and presents five modifications which make the method easier to use and reduce the probability of estimating a larger sample size than is actually required. The method is extended and used to estimate the mean abundance of patchily distributed benthic organisms. The technique can be used to guide the design of any environmental sampling programme, be it physical, chemical or biological, where comparisons between times and/or locations are required. Trade-offs between numbers of replicates and numbers of levels/sites are discussed.

Relationship Between Incidence of Salmonella Contamination Among Pre-scalded, Eviscerated and Post-Chilled Chickens in a Poultry Processing Plant.

The incidence of Salmonella contamination in 11 flocks of chickens was determined at three sites within a poultry processing plant: A, before scalding; B, after evisceration; C, after chilling. The average incidence of Salmonella contamination of flocks ranged from 1.2 to 74.4%, and flock to flock variability among sites was significant. Incidences of Salmonella ranged from 3 to 96% at site A; 0 to 69% at site B; and 0 to 96% at site C. Flocks with a high incidence of Salmonella contamination at site A were also frequently contaminated at sites B and C. By generating regression equations, it was possible to predict the incidence of Salmonella at one of these sites from the incidence at the other sites. The ability to define the interdependence between internal and external Salmonella contamination of chickens provides a basis for developing effective control measures for decreasing the incidence of Salmonella -contaminated retail chickens.