Data Mining for Prediction. Financial Series Case

Hard problems force innovative approaches and attention to detail, their exploration often contributing beyond the area initially attempted. This thesis investigates the data mining process resulting in a predictor for numerical series. The series experimented with come from financial data – usually hard to forecast. One approach to prediction is to spot patterns in the past, when we already know what followed them, and to test on more recent data. If a pattern is followed by the same outcome frequently enough, we can gain confidence that it is a genuine relationship. Because this approach does not assume any special knowledge or form of the regularities, the method is quite general – applicable to other time series, not just financial. However, the generality puts strong demands on the pattern detection – as to notice regularities in any of the many possible forms. The thesis’ quest for an automated pattern-spotting involves numerous data mining and optimization techniques: neural networks, decision trees, nearest neighbors, regression, genetic algorithms and other. Comparison of their performance on a stock exchange index data is one of the contributions. As no single technique performed sufficiently well, a number of predictors have been put together, forming a voting ensemble. The vote is diversified not only by different training data – as usually done – but also by a learning method and its parameters. An approach is also proposed how to speed-up a predictor fine-tuning. The algorithm development goes still further: A prediction can only be as good as the training data, therefore the need for good data preprocessing. In particular, new multivariate discretization and attribute selection algorithms are presented. The thesis also includes overviews of prediction pitfalls and possible solutions, as well as of ensemble-building for series data with financial characteristics, such as noise and many attributes. The Ph.D. thesis consists of an extended background on financial prediction, 7 papers, and 2 appendices.