Cluster Analysis Based on the Central Tendency Deviation Principle

International audienceOur main goal is to introduce three clustering functions based on the central tendency deviation principle. According to this approach , we consider to cluster two objects together providing that their similarity is above a threshold. However, how to set this threshold ? This paper gives some insights regarding this issue by extending some clustering functions designed for categorical data to the more general case of real continuous data. In order to approximately solve the corresponding clustering problems, we also propose a clustering algorithm. The latter has a linear complexity in the number of objects and doesn't require a pre-defined number of clusters. Then, our secondary purpose is to introduce a new experimental protocol for comparing different clustering techniques. Our approach uses four evaluation criteria and an aggrega-tion rule for combining the latter. Finally, using fifteen data-sets and this experimental protocol, we show the benefits of the introduced cluster analysis methods

A study of teachers' views on practical work in secondary schools in England and Wales

Many teachers view practical work as an essential feature of science education. This study examined whether there had been any changes in the relative importance of the aims science teachers assign to the use of practical work, across the full secondary age range (11-18), since the last such national survey undertaken by Kerr 46 years ago. A stratified sample of representative schools was used in which 912 teachers were sent a questionnaire on their views towards the use of practical work in science with a total of 393 responses (42.5) being received. The coefficient of concordance of the various rankings and their significance were calculated, as too were the z-scores. The findings suggest that whilst there have been substantial changes in teachers' views about the use of practical work at Key Stages 4 and 5 (age 15-18) there have been no substantial changes at Key Stage 3 (age 11-14). Furthermore, the results are remarkably similar across subject specialism, teacher gender, and years of teaching experience although this paper will only focus on subject specialism. It appears that changes to the assessment criteria, notably the introduction of Science Investigation (Sc1) at Key Stage 4, and a growing desire amongst educational policy-makers to improve the image of science, have had an effect on how those in the teaching profession perceive the value and aims of practical work particularly at Key Stages 4 and 5. © 2010 Taylor & Francis