Statistics for industrial consumer studies12 June 2009
Test persons interacting with treatments: does it affect our conclusions?12 June 2009, 16:15 – 17:00
Jan Willem Bikker Jan Engel CQM Bikker@cqm.nl To remain competitive in the market place of consumer products, industrial companies start to realize that it is essential to develop products that match the requirements of the modern and critical user. Therefore, user tests play an important role in developing consumer products in industry. Often, these tests are set up and analyzed using techniques from Design of Experiments. Typically, the blocking principle is used and the users are considered as blocks. A common problem is that it is not possible, for each test person, to undergo all treatments; for instance, because the person would get tired or bored. Therefore, the test design is chosen to be a balanced incomplete block design. A standard assumption in this set up, and in the analysis of the experimental data, is that the interaction between blocks and treatments is absent. However, it is our experience from various user tests that these interactions cannot be ignored beforehand. We therefore studied the consequence of block-treatment interactions for the analysis, by ANOVA and linear mixed models, of data from balanced incomplete block designs in user tests. The results from this study will be presented and conclusions will be given.