Statistical Analysis
Data was analysed using SPSS (Version 15.0). Clusters of health related behaviours were identified among 7,350 valid cases using the SPSS TwoStep Clustering algorithm. This algorithm is designed to efficiently handle large datasets, is capable of handling both continuous and categorical variables and has features to aid in determining the optimal number of clusters (SPSS, 2001). A further advantage of the TwoStep Cluster analysis approach is that it identifies which combinations are important from the many logically possible in the data and identifies the types empirically rather than impose them from an a priori scheme.