# School of Design

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## Yuan Li

Research Fellow in Colour Science

0113 343 3717

Clothworkers' Building South | Room 112

BA (Xiamen University) MA (University of Leeds) PhD (University of Leeds)

### Biography

I completed my first degree in Accounting at Xiamen University and came to the UK in 2006 for my Masters (Fashion Marketing) and PhD (Psychophysical Methods) studies. I am currently a post-doctoral researcher on tooth whiteness project at School of Design, University of Leeds. My research interest are psychophysical analytical methods (paired-comparison experimental design and implementation), colour measurement, and colour preference and its influencing factors from socioeconomic dimensions.

### External Appointments

- Program Committee Member, AV chair – IS&T/SID’s Nineteenth Color and Imaging Conference: Colour Science, Systems and Applications (2011)

### PhD Thesis

**Modelling and Evaluation of Paired-Comparison Experiments**

Paired-comparison is a popular method for deriving scale values; scale values are numbers that represent observers‟ psychophysical responses to sets of physical stimuli. The method requires that each observer is presented with pairs of stimuli and is asked which of the pair is greater in terms of the psychophysical property being investigated (for example, which of the pair is lighter). However, it is time consuming (especially when the number of stimuli n is large) since there are n(n-1)/2 possible paired comparisons and all of these must be considered.

It is possible to carry out a so-called incomplete paired-comparison experiment where only a proportion p (0 < p < 1) of the pairs are considered. This thesis primarily addresses questions about the design of incomplete paired-comparison experiments. For instance, what is the smallest value of p and how few observers are required that still allows reliable estimates of the scale values? Monte-Carlo computational simulations were carried out with an ideal observer model assigned with bias. Data were analyzed based on Morrissey‟s least-squares solution. This evaluation indicated that satisfactory results can be obtained with as few as 30% (in the case where each observer compared the same pairs) or 10% (in the case where each observer compared different pairs) of paired comparisons. However, the actual proportion of paired comparisons depends upon k (the number of observers) and n (the number of stimuli). A table was produced that indicated the value of p required (for various values of n and k) required to give a certain level of performance (this was somewhat arbitrarily defined as r^2 = 0.95; where r is the expected Pearson product-moment correlation coefficient between the estimated scale values and their true values).

A psychophysical experiment was conducted employing both the paired-comparison method and the categorical judgement method to estimate scale values. Results from the paired-comparison experiment were consistent with those predicted from the Monte-Carlo computational simulations. The paired-comparison experiment was analysed for various values of p and its performance compared with results from the categorical judgement method where n = 10. For the paired-comparison method where p = 1 (where all of the pairs are considered) the estimated scale values were more accurate than those from the categorical judgement experiment; however, as p reduces, the accuracy of the scale values from the paired-comparison method also reduced. The point where the two techniques gave broadly similar performance was at p = 0.2 (where each observer compared different sets of pairs) or p = 0.4 (where all observers compared the same set of pairs).

### Professional Practice

*Presentations*

Li Y. Presentation of ‘Monte-Carlo simulations for paired-comparison experiments’ at the 20th Congress of the International Color Association, Taipei, Taiwan, in September 2012.

Li Y. Presentation of ‘Models estimation for incomplete paired-comparison experiments based on least squares solution’ at the 3rd International Conference on Appearance, Edinburgh, UK, in April 2012.

Li Y. Presentation of ‘Evaluation of incomplete paired-comparison experiments’ at the IS&T/SID’s Nineteenth Color and Imaging Conference, San Jose, USA, November 2011.

Li Y. Presentation of ‘Colour preference in context’ at Connections in culture, society and innovation, Leeds (UK), August 2011, **invited talk**.

Li Y. Presentation of ‘Social factors effects on colour preference’ at CREATE (Colour Research for European Advanced Technology Employment) – Communicating Colour, Pannon University, Veszprem, Hungary, in May 2009.

Li Y. Presentation of ‘Colour preference on logo design’ at CREATE (Colour Research for European Advanced Technology Employment) – New Ways to use Print Technology: (On Fabric), University of Ulster, Belfast, Northern Ireland, in October 2008.