Computer and Information Science November, 2008 3 An Alternative Analysis of Two Circular Variables via Graphical Representation: An Application to the Malaysian Wind Data Yong Zulina Zubairi (Corresponding author) Centre for Foundation Studies in Science University of Malaya 50603 Kuala Lumpur, Malaysia Tel: 6-03-7967-5971 E-mail:yzulina@um.edu.my Fakhrulrozi Hussain Institutes of Postgraduates Studies University of Malaya 50603 Kuala Lumpur, Malaysia Tel: 6-03-7967-4263 E-mail:fakhrul@perdana.um.edu.my Abdul Ghapor Hussin Centre for Foundation Studies in Science University of Malaya 50603 Kuala Lumpur, Malaysia Tel: 6-03-7967-5821 E-mail:ghapor@um.edu.my Abstract The relationship between variables is vital in data analysis. The scatter plot, for instance, gives an easy preliminary exploratory analysis for finding relationship between two variables, if any. Statistical method such as correlation and linear relationship are standard tools in most statistical packages. For circular variables that take value on the circumference of a circle, the analysis however is different from those of the Euclidean type variables because circumference is a bounded closed space. Unlike linear variable, standard statistical packages for circular variables are limited. This paper proposes a graphical representation of two circular variables as a preliminary analysis using the MATLAB environment. A plot called Spoke plot is developed to visually display relationship between two circular variables and linear correlation. As an illustration, the Malaysian wind data is used in the analysis. This new type of representation promises an alternative approach in the preliminary analysis of circular data. Keywords: Spoke plot, Wind data, Circular, Correlation, Linear Relationship 1. Introduction Circular variables take values on the circumference of a circle and thus are bounded in a closed space. Unlike the usual Euclidean type variables, the analysis of directional data is different. Further readings in circular variables can be found in Fisher (1993) and Mardia (1999, 1972). A number of environmental data are circular in nature such as wave, wind direction, compass bearing, clock and others. Statistical softwares devoted to the analysis of circular variable are limited. At present, there are only two softwares in the market namely AXIS (Handerson et el., 2002) and ORIANA (Oriana Software, 2007), that offer some statistical analysis of circular variable on a window-based environment. Although these packages offer a range of graphical and analytical techniques required for statistical analysis of circular data, they have some limitations. For example, further analysis such as statistical inference, analyzing grouped data sets, circular plots of the corresponding probability density functions as well as regression and correlation of circular data are not available in the existing packages. In this study, an alternative diagrammatical representation of correlation and linear relationship