Lena Zetterqvist

Statistical estimation and interpretation of trends in water quality time series

Three approaches to trend analysis of water quality time series are discussed: (1) seasonal model, with a test for trend based on ranks of observations, with observations assumed to be m dependent; (2) transfer function noise model, in which covariate series may be included by means of transfer functions, with the remaining noise modeled as a seasonal autoregressive moving average process; and (3) component model, with the noise decomposed into series which describe trends, and irregular and seasonal variation. Models are studied with regards to their ability to include covariate series, possibility of interpretation of trends, treatment of seasonal variation and serial dependence, and robustness for outliers. We regard the component model being the most realistic and the most informative of the three approaches. Models are applied to series of monthly phosphorus concentration in the Ljungbyan River in Southern Sweden.

Statistics for chemistry students - how to make a statistics course useful by focusing on applications

By putting emphasis on applications in two basic statistics courses for chemistry students and chemical engineering students we have enhanced student motivation and increased student activity. In addition to a traditional in-class exam, the students complete a take-home project where statistical problems relevant to chemists are discussed. We give several examples of the course and project material. The main difference between the two courses is that the first is optional, attracting approximately 15 students, while the second is compulsory with approximately 100 students. We discuss how the different requirements affect the learning situation and how separate strategies of teaching have to be developed for the small class and large class situations, respectively.

Sensitivity of mongolian gerbils to trichloroethylene exposure during neonatal growth

Continuous exposure of young mongolian gerbils to trichloroethylene (230 ppm) was started at different times during the first month of life. The onset of exposure was accompanied by an increased number of deaths among the pups and by an immediate reduction in growth rate. The proportion of dead pups was greatest when exposure was started at birth, and decreased rapidly with increasing age at onset of exposure. Growth rate was partially restored approx. 1 week after the onset of exposure. After weaning the effect of the exposure on growth decreased, and the variation in the effect among different litters was considerably reduced. The enhanced sensitivity of the pups to trichloroethylene (TCE) exposure is believed to be due to a disturbance in the mother-offspring relationship.