Reliability of selected table tennis performance indicators

Over the last few years, scientific research in sport has focused in detail on a branch of performance analysis, namely notational analysis. Notational analysis allows the collection of interesting data about matches and also provides good feedback information to improve technical and tactical aspects. However, the analysts have to select the most important performance indicators and first of all, tehy must evaluate the reliability of the data. The aim of this study is to evaluate the intra and inter-observer reliability of some of the most important performance indicators in table tennis. Inter-observer reliability: 10 highly experienced coaches (third national level, high level) have analysed the first set of men's table tennis and noted: player footwork/step, stroke modality and impact point of the ball on the table (6 areas). Intra and inter-observer reliability have been evaluated by Krippendorff's Alpha, calculated through the statistical software R. Krippendorff's Alpha could range from 1 (perfect reliability) to -1 (total disagreement). A good reliability is attained for Alpha= 0.8. Concerning the inter-observer reliability, the values of Alpha were 0.894 for different kinds of stroke, and 0.469 for efficacy (3 levels: +, 0 and -). The intra-observer reliability analysis showed the following values: Alpha= 0.092 for strokes, Alpha=0.99 for different kinds of step and Alpha = 0.997 for impact point fo the ball on the table. The only performance indicators without good reliability were connected with the evaluation of the efficacy of intermediate strokes. The other indicators, assessed by inter and intra-operator comparisons, showed very good reliability. These results allow us to state that the selected performance indicators can be taken into account in table tennis notational analysis.