ENBIS-8 in Athens

21 – 25 September 2008 Abstract submission: 14 March – 11 August 2008

What if test persons don't behave as blocks and actually do interact with treatments?

23 September 2008, 12:00 – 12:20


Submitted by
Jan-Willem Bikker
Jan-Willem Bikker, and Jan Engel
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.

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